Waterproof stretchable optoelectronics

ABSTRACT

Described herein are flexible and stretchable LED arrays and methods utilizing flexible and stretchable LED arrays. Assembly of flexible LED arrays alongside flexible plasmonic crystals is useful for construction of fluid monitors, permitting sensitive detection of fluid refractive index and composition. Co-integration of flexible LED arrays with flexible photodetector arrays is useful for construction of flexible proximity sensors. Application of stretchable LED arrays onto flexible threads as light emitting sutures provides novel means for performing radiation therapy on wounds.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/046,191, filed Mar. 11, 2011, which claims the benefit of andpriority to U.S. Provisional Application No. 61/388,529 filed on Sep.30, 2010; U.S. Provisional Application No. 61/313,397 filed on Mar. 12,2010; U.S. Provisional Application No. 61/314,739 filed on Mar. 17,2010. U.S. patent application Ser. No. 13/046,191 is also acontinuation-in-part of U.S. spplication Ser. No. 12/968,637 filed onDec. 15, 2010; International Application No. PCT/US10/60425 filed Dec.15, 2010; U.S. patent application Ser. No. 12/892,001 filed on Sep. 28,2010, now U.S. Pat. No. 8,666,471 and International Application No.PCT/US10/50468 filed Sep. 28, 2010. U.S. application Ser. No. 12/968,637and International Application No. PCT/US10/60425 also claim the benefitof priority to U.S. Provisional Application No. 61/313,397; U.S.Provisional Application No. 61/286,921 and U.S. Provisional ApplicationNo. 61/388,529 filed on Sep. 30, 2010. U.S. patent application Ser. No.12/892,001, now U.S. Pat. No. 8,666,471, and International ApplicationNo. PCT/US10/50468 also claim the benefit of priority to U.S.Provisional Application No. 61/314,739. Each of the above-identifiedapplications is hereby incorporated by reference in its entirety to theextent not inconsistent herewith.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States governmental support from theNational Science Foundation under grant DMI-0328162, the U.S. Departmentof Energy under Award No. DE-FG02-07ER46471, the U.S. Army ResearchLaboratory and the U.S. Army Research Office under contract number W911NF-07-1-0618 and by the DARPA-DSO and the National Institutes of HealthP41 Tissue Engineering Resource Center under award number P41 EB002520.The U.S. government has certain rights in the invention.

BACKGROUND

This invention is in the field of stretchable and flexible electronics.This invention relates generally to flexible and stretchable electronicsadapted for use in biomedical, sensing and robotics applications.

Many established forms of inorganic light emitting diodes (LEDs) andphotodetectors (PDs) incorporate rigid, flat and brittle semiconductorwafers as supporting substrates, thereby restricting the ways that thesedevices can be used. Research in organic optoelectronic materials ismotivated, in part, by the potential for alternative applicationsenabled by integration of thin film devices on flexible sheets ofplastic. Many impressive results have been achieved in recent years,several of which are moving toward commercialization.

There is growing interest in the use of organic and inorganicmicro/nanomaterials and devices in similarly unusual forms on plastic,paper, textile, rubber, and other flat or curved substrates. Forexample, European Patent Application EP 1467224 discloses a flexibleoptical proximity detector which utilizes organic semiconductorelements.

Additionally, sealing of electronic devices permits a variety of uses inbiological environments. For example, International Patent ApplicationPublication WO 2009/076088 discloses an implantable optical sensordevice which is hermetically sealed.

A variety of platforms are available for printing structures on devicesubstrates and device components supported by device substrates,including nanostructures, microstructures, flexible electronics, and avariety of other patterned structures. For example, a number of patentsand patent applications describe different methods and systems formaking and printing a wide range of structures, including U.S. Pat. Nos.7,705,280, 7,195,733, 7,557,367, 7,622,367 and 7,521,292, U.S. PatentApplication Publication Nos. 2009/0199960, 2007/0032089, 2008/0108171,2008/0157235, 2010/0059863, 2010/0052112, 2010/0283069 and 2010/0002402,U.S. patent application Ser. No. 12/968,637 filed Dec. 15, 2010 and Ser.No. 12/892,001 filed Sep. 28, 2010; all of which are hereby incorporatedby reference in their entireties to the extent not inconsistentherewith.

SUMMARY

Provided herein are a variety of stretchable and flexible opticaldevices incorporating micro-scale inorganic semiconductor elements, andmethods utilizing stretchable and flexible devices incorporatingmicro-scale inorganic semiconductor elements. The devices describedherein are useful in biomedical applications, for example inapplications for sensing, treating, repairing and actuating biologicaltissue. A number of the devices described herein permit interaction withbiological tissues by incorporating a waterproof component protectingdevice elements from exposure to water from the biological environment,for example presenting an electrical short circuit caused by contact ofwater from the biological environment. A number of the devices describedherein permit interaction with biological tissues by incorporating abarrier layer component for limiting a net leakage current from theflexible or stretchable electronic circuit to the biological environmentto an amount that to an amount which does not adversely affect thetissue and/or biological environment. The unique substrates andapplications disclosed further permit novel uses as sensors andactuators in robotics, medical and biomedical applications.

In embodiments, the devices described herein provide multiple componentintegrated device configurations, for example devices includingcombinations of active sensing components, active actuating componentsand/or passive components. Useful active and passive components includeflexible or stretchable electronic devices. Useful passive devicecomponents include structural device elements, for example sutures,threads, flexible substrates, stretchable substrates, barrier layers,encapsulation layers, microstructured or nanostructured elements andoptical elements. Multiple component device integration is achieved insome embodiments by contacting one device component, such as a flexibleor stretchable electronic device on a first substrate with a seconddevice component. In certain embodiments, adhesives or adhesive layersare provided between the individual components in a multiple componentdevice to unite the components a single integrated device. Optionally,an individual component in a multiple component device has an internaladhesive layer. In certain embodiments, the individual components areeach provided on individual substrates with an adhesive layer providedbetween the substrates to unite the components into a single integrateddevice. In certain embodiments, the individual components areencapsulated to unite the components into a single integrated device. Incertain embodiments, one component is laminated on top of anothercomponent to unite the components into a single integrated device. Incertain embodiments, one component is printed on top of anothercomponent to unite the components into a single integrated device. Incertain embodiments, one component is printed on top of an encapsulatedcomponent to unite the components into a single integrated device.Multiple component device integration is achieved in some embodiments byprocessing in which a component, such as a lenses array, optical filter,polarizer, etc., is molded or embossed directly into another componentor molded onto a layer provided on another component such as on a layerlaminated on another layer. In an embodiment, an optical component ismolded into an intermediate elastomer layer provided on a flexible orstretchable electronic device, for example, via a replica molding ornano-imprinting molding technique.

In a first aspect, a multiple component integrated device is abiomedical device. In one embodiment, provided are biomedical devicesuseful for treating a tissue in a biological environment, such as anin-vivo biological environment and/or a biological environmentcomprising a conductive ionic solution. Such devices are useful, forexample, for performing therapy on a tissue, for closing openings orwounds in a tissue, for treating medical conditions and for tissuesensing and actuation applications. Devices of this aspect includesutures incorporating electronic devices or electronic circuits forinteraction with tissues in biological environments.

In a specific embodiment, a device of this aspect comprises a suturehaving an external surface, a flexible or stretchable electronic circuitsupported by the external surface of the suture, and a barrier layer atleast partially encapsulating the flexible or stretchable electroniccircuit. In a specific embodiment, the flexible or stretchableelectronic circuit comprises one or more inorganic semiconductorelements, such as inorganic semiconductor elements having an averagethickness less than or equal to 100 μm. In a specific embodiment, adevice of this aspect further comprises a controller in electricalcommunication with the flexible or stretchable electronic circuit. In aspecific embodiment, a device of this aspect further comprises aflexible or stretchable substrate positioned between the externalsurface of the suture and the flexible or stretchable electroniccircuit, for example a substrate comprising an elastomer, such as PDMS.In an embodiment, the components of the biomedical device, such as theflexible or stretchable electronic device are encapsulated by a barrierlayer comprising an elastomer material.

In embodiments, one component of a multiple component integrated deviceis a flexible or stretchable substrate, for example a stretchable orflexible substrate positioned in contact with another component of amultiple component integrated device. In specific embodiments, devicesdescribed herein further comprise an additional flexible or stretchablesubstrate positioned between a flexible or stretchable electronic deviceand the supporting surface, for example a PDMS substrate. In specificembodiments, a flexible or stretchable substrate has an averagethickness selected over the range of 0.25 μm to 1000 μm, or an averagethickness less than or equal to 100 μm. Useful flexible or stretchablesubstrates include those having an average modulus selected over therange of 0.5 KPa to 10 GPa. In a specific embodiment, a flexible orstretchable substrate has a substantially uniform thickness over aflexible or stretchable electronic circuit. In embodiments, a flexibleor stretchable substrate has a thickness that varies selectively alongone or more lateral dimensions over a flexible or stretchable electroniccircuit. Optionally a flexible or stretchable substrate is a flexible orstretchable mesh structure. Useful flexible or stretchable substratesinclude those comprising a biocompatible material, a bioinert material,a bioresorbable material or any combination thereof. Specific materialsuseful for flexible or stretchable substrates of this aspect includethose comprising material selected from the group consisting of apolymer, an inorganic polymer, an organic polymer, a plastic, anelastomer, a biopolymer, a thermoset, a rubber, fabric, paper and anycombination of these. In specific embodiments, the flexible orstretchable substrate comprises an elastomer, PDMS, parylene, orpolyimide.

In embodiments, one component of a multiple component integrated deviceis a suture. In embodiments, sutures useful with the devices and methodsdescribed herein include sutures comprising a fiber or a thread. Usefulsutures also include those comprising a biocompatible material, abioinert material or a combination of biocompatible and bioinertmaterials. In a specific embodiment, a suture comprises a bioresorbablematerial. Specific sutures useful with the devices and methods describedherein include those comprising a material selected from the groupconsisting of a biopolymer, a synthetic polymer, a natural fiber, asynthetic fiber, a protein, a polysaccharide, silk and any combinationof these. Useful sutures further include sutures used in medicalprocedures. In a specific embodiment, useful sutures include thosecomprising a polymer such as polyglycolic acid (Biovek), polylacticacid, polydioxanone, or caprolactone. In a specific embodiment, a suturecomprises silk. In a specific embodiment, a suture comprisespolypropylene, polyester or nylon. In a specific embodiment, a suturecomprises stainless steel.

In specific embodiments, a suture has an average diameter over itslength less than or equal to 1000 μm, such as those having averagediameters selected over the range of 1 μm to 1000 μm, optionally 10 μmto 1000 μm, optionally 100 μm to 1000 μm or any sub-ranges thereof.Suture in the present devices include those having a tensile strengthselected over the range of 50 MPa to 1000 MPa, preferably for someembodiments 100 MPa to 1000 MPa, and preferably for some embodiments 200MPa to 1000 MPa In an embodiment, a suture has a length selected overthe range of 1 cm to 100 m. Useful sutures include those which arestretchable or flexible, for example those having an average modulusselected over the range of 0.5 kPa to 10 GPa, those having a netflexural rigidity less than or equal to 1×10⁻⁴ Nm, those having a netbending stiffness less than or equal to 1×10⁸ GPa um⁴, or anycombination of these properties.

In an exemplary embodiment, a device, such as a suture, has an externalsurface which is nanostructured or microstructured. In embodiments, anexternal surface of a device is patterned using replica molding ornano-imprint lithography. Nanostructured and microstructured suturesinclude those having a plurality of nanostructures or microstructureswhich accommodate a flexible or stretchable electronic circuit or acomponent thereof. In an embodiment, the external surface of a suture isprovided in conformal contact with at least a portion of a flexible orstretchable electronic circuit. In an embodiment, the external surfaceof a suture is provided in physical contact with at least a portion of aflexible or stretchable electronic circuit. Optionally, sutures usefulwith the devices and methods described herein have external surfaceshaving one or more microstructured or nanostructured openings, channels,vias, receiving surfaces, relief features, optically transmissiveregions, optically opaque regions or selectively permeable regions thatare permeable to one or more target molecules.

In embodiments, one component of a multiple component integrated deviceis a layer, such as a barrier layer, having a nanostructured ormicrostructured surface, optionally exposed to the tissue and/orbiological environment. In an embodiment, for example, a multiplecomponent integrated device comprises a barrier layer having amicrostructured or nanostructure external surface providing a pluralityof raised or recessed features exposed to the tissue or biologicalenvironment, such as channels, vias, pores, opening, windows, etc.Useful nanostructured or microstructured components include thosepatterned using replica molding or nano-imprint lithography techniques.In certain embodiments, a nanostructured or microstructured componentprovides useful properties to a device, for example a surface thatpromotes cell growth, a surface that inhibits cell growth, a surfacewith enhanced wetting properties, a surface with reduced wettingproperties, a surface with altered optical properties.

Optionally, an adhesive layer is provided between a flexible orstretchable electronic circuit and a surface, such as the externalsurface of a suture. In embodiments, for example, an adhesive layer isdeposited over at least a portion of a surface, such as an externalsurface of a suture, for example an elastomeric layer such as a PDMSlayer. In embodiments, an adhesive layer deposited on a surface ispatterned using replica molding or nano-imprint lithography. Adhesivelayers are further useful for enhancing the attachment of elements to asurface during a printing process, such as dry transfer contactprinting. In some embodiments, adhesives improve the structural ormechanical integrity of a device, for example by preventing, reducing orlimiting motion between two device elements in contact with theadhesive. In some embodiments, the adhesive layer functions to laminateone or more layers in a multilayer device, such as a 3D multilayer LEDarray comprising individually encapsulated 2D LED arrays. In someembodiments, the adhesive layer functions to at least partiallyencapsulate one or more device components.

Also provided are methods of making biomedical devices. A method of thisaspect comprises the steps of providing a flexible or stretchable suturehaving an external surface, rolling the flexible or stretchable sutureover a plurality of inorganic semiconductor elements such that one ormore inorganic semiconductor elements are transferred to an externalsurface of the flexible or stretchable suture, and encapsulating atleast a portion of the one or more transferred inorganic semiconductorelements with a barrier layer. In another embodiment, a method of thisaspect comprises the steps of: providing a flexible or stretchablesuture having an external surface, assembling a plurality of printableinorganic semiconductor elements on an external surface of the flexibleor stretchable suture using dry transfer contact printing, andencapsulating at least a portion of the one or more transferredinorganic semiconductor elements with a barrier layer. Another method ofthis aspect comprises the steps of providing a flexible or stretchablesuture, transfer printing one or more inorganic semiconductor elementsto an external surface of the flexible or stretchable suture, andencapsulating at least a portion of the one or more transfer printedinorganic semiconductor elements with a barrier layer. Optionally,methods of this aspect further comprise providing an adhesive layer onan external surface of the suture, for example, wherein the adhesivelayer comprises an elastomer layer such as a PDMS layer. In specificembodiments of these aspects, the barrier layer comprises abioresorbable material, a biocompatible material, or a combination ofbioresorbable and biocompatible materials.

In another aspect, methods are provided for treating a tissue in abiological environment. A method of this aspect comprises the steps ofproviding the tissue and contacting the tissue with a biomedical device,such as a device described herein, for example a biomedical devicecomprising a suture. In embodiments of this aspect, the tissue has anopening, a wound, or a surgical incision and the step of contacting thetissue with the biomedical device comprises closing the opening, woundor surgical incision, for example by stitching or otherwise sewing upthe opening. A specific method of treating a tissue comprises thermally,optically or electrically activating a barrier layer of a biomedicaldevice to release one or more pharmaceutical compositions at leastpartially encapsulated by or otherwise incorporated into the barrierlayer into a biological environment, for example including the tissue.In a specific embodiment, actuation of one or more inorganicsemiconductor elements changes a permeability of, degrades or melts atleast a portion of a barrier layer, thereby releasing at least a portionof the one or more pharmaceutical compositions into a biologicalenvironment.

A specific method for performing therapy on a wound of a tissuecomprises the steps of providing the tissue having the wound, contactingthe wound with a biomedical device, such as a biomedical devicecomprising a suture having an external surface, a flexible orstretchable array of light emitting diodes supported by the externalsurface of the suture, and a barrier layer at least partiallyencapsulating the flexible or stretchable electronic circuit, andexposing the wound to electromagnetic radiation generated by theflexible or stretchable array of light emitting diodes.

Some methods of these aspects further comprise a step of actuating orsensing the tissue in contact with the biomedical device. Forembodiments of this aspect where the biomedical device comprises anarray of light emitting diodes, the array of light emitting diodesgenerate electromagnetic radiation and the method further comprises astep of exposing the tissue to the electromagnetic radiation orvisualizing the electromagnetic radiation.

In an embodiment, a biomedical device further comprises one or moresensors supported by the external surface of the suture, such as one ormore thermal sensors (e.g., thermocouple, thermistor, etc.), opticalsensors (e.g., photodetector or photodetector array), or electronicsensors (e.g., measurement of current or voltage), optionally providedin a partially or completely encapsulated configuration, such as havingan elastomeric encapsulating layer. In an embodiment, for example, adevice of this aspect further comprises one or more temperature sensorsand/or or heaters supported by the external surface of the suture. In anembodiment, a device of this aspect further comprises one or moreoptical components supported by the external surface of the suture andoptionally provided on top of the flexible or stretchable electronicdevice. In an embodiment, for example, the device further comprises oneor more molded or embossed optical components in optical communicationwith the flexible electronic device, such as lenses, diffusers or arraysthereof. A method for sensing or actuation of a tissue comprises thesteps of providing the tissue, contacting the tissue with a biomedicaldevice comprising a flexible or stretchable array of light emittingdiodes (LEDs) and a flexible or stretchable array of photodetectors(PDs), actuating at least a portion of the flexible or stretchable arrayof LEDs to generate and expose the tissue electromagnetic radiation toexpose and sensing electromagnetic radiation scattered, reflected oremitted by the tissue with at least a portion of the flexible orstretchable PD array. In specific embodiments, the electromagneticradiation has a wavelength or wavelength range within the Optical windowor therapeutic window of the biological tissue. As used herein “opticalwindow” or “therapeutic window” of a biological tissue refers to aregion of the electromagnetic spectrum over which electromagneticradiation has a substantial penetration depth in the biological tissue,such as a wavelength range of 650 nm to 1300 nm. In specificembodiments, the electromagnetic radiation has a wavelength of 680 nm ora wavelength range including 680 nm. In specific embodiments, theelectromagnetic radiation has a wavelength of 940 nm or a wavelengthrange including 940 nm. In specific embodiments, the electromagneticradiation has a wavelength useful for sensing the extent of oxygenationof blood in the tissue.

In another aspect, a multiple component integrated device is provided inelectrical communication with a controller. Useful controllers includethose comprising a microprocessor. Controllers useful with the devicesand methods described herein include controllers which perform one ormore specific functions such as a diagnostic and/or therapeuticfunction. In a specific embodiment, a controller provides, directly orindirectly, a current or a voltage to an electronic circuit. In aspecific embodiment, a controller receives, directly or indirectly, acurrent or a voltage from an electronic circuit or informationcorresponding to or derived from a current or voltage, for example acurrent generated by a photodetector in response to receipt ofelectromagnetic radiation. Useful controllers permit automatic,autonomous or manual operation of the devices described herein. In oneembodiment, a controller receives information corresponding to anintensity of electromagnetic radiation received by a photodetector andprovides to an electronic circuit a current or voltage having amagnitude derived from the intensity of the electromagnetic radiationreceived by the photodetector. In one embodiment, a controller receivesinformation corresponding to an intensity of electromagnetic radiationreceived by a photodetector and provides to an electronic circuit acurrent or voltage that actuates at least a portion of an electroniccircuit, for example a light emitting diode or a microelectromechanicaldevice.

In embodiments, a multiple component integrated device comprises one ormore conductive electrical interconnects providing electricalcommunication between an electronic circuit of a multiple componentintegrated device and a controller. Useful electrical interconnectsinclude, but are not limited to, wire bonded interconnects,interconnects comprising a ribbon cable, interconnects comprisinglithographically patterned conductors and combinations of these. Inembodiments, the controller is provided in wired or wireless, one-way ortwo-way communication with an electronic circuit.

Devices described herein include those having one or more componentscomprising one or more bioresorbable materials. For example, providedare biomedical devices wherein the suture component is a bioresorbablematerial; and/or wherein the barrier layer comprises a bioresorbablematerial; and/or wherein the flexible or stretchable substrate componentcomprises a bioresorbable material. A variety of bioresorbable materialsare useful in the present devices, including materials that areefficiently processed and/or remodeled without formation of biologicallyactive, toxic and/or harmful byproducts upon contact with a biologicalenvironment. Useful bioresorbable materials include, for example, abiopolymer (e.g., protein, peptide, carbohydrate, polynucleotide, etc.),a synthetic polymer, a protein, a polysaccharide, silk,poly(glycerol-sebacate) (PGS), polydioxanone, poly(lactic-co-glycolicacid) (PLGA), polylactic acid (PLA), collagen, chitosan, fibroin, andcombinations of these. Useful silk materials for components of thedevices described herein include, for example, silkworm fibroin,modified silkworm fibroin, spider silk, insect silk, recombinant silk,and any combination of these. As used herein, modified silkworm fibroinrefers to a polymer composition that is derived via chemicalmodification of silkworm fibroin.

The physical dimensions and physical properties of components comprisinga bioresorbable material are important parameters for supporting a rangeof device functionalities and compatibility with different tissue types.In some embodiments, the component comprising a bioresorbable materialhas a thickness less than or equal to 10,000 μm, and optionally in someembodiments less than or equal to 1000 μm, and optionally in someembodiments less than or equal to 100 μm, and optionally in someembodiments less than or equal to 10 μm; and optionally in someembodiments less than or equal to 1 μm. Use of a thin componentcomprising a bioresorbable material (e.g., thickness less than or equalto 100 μm, optionally less than or equal to 10 μm and optionally lessthan or equal to 1 μm) is useful for providing a flexible, or otherwisedeformable device capable of establishing conformal contact with a widerange of tissue types, including tissues having complex, highlycontoured surfaces. In some embodiments, the component comprising abioresorbable material has a thickness selected over the range of 100 nmand 10000 μm, optionally for some applications selected over the rangeof 1 μm and 1000 μm, and optionally for some embodiments selected overthe range of 1 μm and 10 μm. In some embodiments, the composition andphysical properties (e.g., Young's modulus, net bending stiffness,toughness, etc.) of the component comprising a bioresorbable materialare selected to provide sufficient structural support for the electronicdevice component, while also providing an ability to achieve a highdegree of conformal contact upon deployment. In some embodiments, thecomponent comprising a bioresorbable material is a low modulus layer.Alternatively, useful device include those having a component comprisinga bioresorbable material that is a high modulus layer. In someembodiments, for example, the component comprising a bioresorbablematerial has a Young's modulus less than or equal to 10 GPa, preferablyfor some applications a Young's modulus less than or equal to 100 MPa,optionally for some applications less than or equal to 10 MPa. In someembodiments, for example, the component comprising a bioresorbablematerial has a Young's modulus selected over the range of 0.5 MPa and 10GPa, and optionally for some applications selected over the range of 0.5MPa and 100 MPa, and optionally for some applications selected over therange of 0.5 MPa and 10 MPa. In some embodiments, for example, thecomponent comprising a bioresorbable material has a net bendingstiffness less than or equal to 1×10⁹ GPa μm⁴, optionally for someapplications less than or equal to 1×10⁷ GPa μm⁴ and optionally for someapplications less than or equal to 1×10⁶ GPa μm⁴. In some embodiments,for example, the component comprising a bioresorbable material has a netbending stiffness selected over the range of 0.1×10⁴ GPa μm⁴ and 1×10⁹GPa μm⁴, and optionally for some applications between 0.1×10⁴ GPa μm⁴and 5×10⁵ GPa μm⁴.

In some biological environments, such as an in vivo biologicalenvironment, the degradation of the bioresorbable material occurs viaenzymatic degradation, for example, via protease mediated degradation.In addition, degradation occurs in some embodiments from the surfaces ofthe bioresorbable material that are exposed to the biologicalenvironment having degradation enzymes present, such as at the interfacewith a tissue and/or biological fluid. Accordingly, certain parametersof the bioresorbable material may be selected to effectively control theresorption rate. In an embodiment, the chemical composition, physicalstate and/or thickness of the bioresorbable material is selected so asto control the resorption rate. In an embodiment, for example, thebioresorbable material comprises a biopolymer exhibiting a usefulresorption rate for a selected biological environment, such as a silkbiopolymer exhibiting a useful resorption rate. Useful bioresorbablematerials include those comprising amorphous materials, crystallinematerials, partially amorphous materials and partially crystallinematerials. In an embodiment, devices described herein include an atleast partially crystalline material, wherein the extent ofcrystallinity of the bioresorbable material is selected to provide auseful and/or preselected resorption rate for a selected biologicalenvironment and device application. In some embodiments, the larger thedegree of crystallinity of the bioresorbable material the slower theresorption rate when provided in contact with the target tissue. Forexample, devices described herein include those having a bioresorbablematerial with a degree of crystallinity less than or equal to 55%, andoptionally a degree of crystallinity less than or equal to 30% andoptionally a degree of crystallinity less than or equal to 20%, andoptionally a degree of crystallinity less than or equal to 5%. Forexample, devices described herein include those having a bioresorbablematerial with a degree of crystallinity selected over the range of 0 to55%, and optionally for some embodiments a degree of crystallinityselected over the range of 1 to 30%, and optionally for some embodimentsa degree of crystallinity selected over the range of 5 to 20%. As usedherein, 0% crystallinity refers to an entirely amorphous material andthe given degree of crystallinity corresponds to the amount of amaterial provided in a crystalline state relative to the total amount ofmaterial. In some embodiments, for example those having a silkbioresorbable material, the degree of crystallinity refers to the betasheet content of the silk bioresorbable material.

In some embodiments, implantable biomedical devices advantageouslyutilize silk as a bioresorbable material. Silk is biocompatible,FDA-approved, optically transparent, mechanically robust (highmechanical modulus and toughness), and flexible in thin film form. It isalso compatible with aqueous processing, which preserves sensitiveelectronic functions, and amenable to chemical and biologicalfunctionalization. The presence of diverse amino acid side chainsfacilitates coupling chemistry for functionalizing silks. Silk is alsowater soluble with programmable rates of proteolytic biodegradation(yielding non-inflammatory amino acids) over a range from minutes tohours to years.

Some other natural polymers that exhibit properties similar to oranalogous to silk include, but are not limited to, chitosan, collagen,gelatin, agarose, chitin, polyhydroxyalkanoates, pullan, starch (amyloseamylopectin), cellulose, hyaluronic acid, or any combination of these.

Silk may be obtained from various natural sources, for example, from thesilkworm Bombyx mori or from the spider Nephila clavipes. Silk solutionsused in accordance with embodiments described herein may be obtained,for example, from a solution containing a dissolved silkworm silk (e.g.from Bombyx mori), a dissolved spider silk (e.g. from Nephila clavipes),or from a solution containing a recombinant silk, such as from bacteria,yeast, mammalian cells, transgenic animals, or transgenic plants.

In an embodiment, the silk of the bioresorbable material may be silkfibroin protein, which consists of layers of antiparallel beta sheetsand has a primary structure consisting mainly of the recurrent aminoacid sequence (Gly-Ser-Gly-Ala-Gly-Ala)_(n). Fibroin is known to arrangeitself in three structures, called silk I, II, and III. Silk I is thenatural, amorphous form of fibroin, as emitted from the Bombyx mori silkglands. Silk II refers to the crystalline arrangement of fibroinmolecules in spun silk, which has greater strength. Silk III is formedprincipally in solutions of fibroin at an interface (i.e. air-waterinterface, water-oil interface, etc.). In the disclosed implantablebiomedical devices, silk I, II and/or III may be used.

In another aspect, a multiple component integrated device is a proximitysensor device. Proximity sensor devices are useful, for example, inmethods for sensing a distance between two objects, for example in abiological environment. A device of this aspect comprises a flexible orstretchable substrate, one or more flexible or stretchable lightemitting diode (LED) arrays supported by the flexible or stretchablesubstrate, one or more flexible or stretchable photodetector (PD) arrayssupported by the flexible or stretchable substrate, and one or morebarrier layers at least partially encapsulating the one or more flexibleor stretchable LED arrays, at least part of the one or more flexible orstretchable PD arrays, or at least parts of both. In embodiments, theone or more flexible or stretchable LED arrays comprise a large areaarray. In embodiments, the one or more flexible or stretchable PD arrayscomprise a large area array. In a specific embodiment, a device of thisaspect further comprises a controller in electrical communication withthe one or more flexible or stretchable LED arrays and/or PD arrays.Optionally, the one or more flexible or stretchable LED arrays and theone or more flexible or stretchable PD arrays are provided in one ormore individually encapsulated layers in a multilayer stacked geometry.

A method of this latter aspect for sensing a distance between twoobjects comprises the steps of providing a first object having a firstsurface, providing a proximity sensor on the first surface, theproximity sensor comprising: a flexible or stretchable substrate, one ormore flexible or stretchable LED arrays supported by the flexible orstretchable substrate, each flexible or stretchable LED array comprisingone or more inorganic LEDs having an average thickness less than orequal to 100 μm, and one or more flexible or stretchable PD arrayssupported by the flexible or stretchable substrate, each flexible orstretchable PD array comprising one or more inorganic semiconductorelements having an average thickness less than or equal to 100 μm, oneor more barrier layers at least partially encapsulating the one or moreflexible or stretchable LED arrays and the one or more flexible orstretchable PD arrays, wherein the barrier layer prevents water from abiological environment from contacting at least a portion of theinorganic LEDs of the one or more flexible or stretchable LED arrays andat least a portion of the inorganic semiconductor elements of the one ormore flexible or stretchable PD arrays; providing a current, voltage orelectromagnetic energy to the one or more flexible or stretchable LEDarrays, thereby producing electromagnetic radiation from the one or moreflexible or stretchable LED arrays; providing a second object at adistance from the first object, the second object positioned in opticalcommunication with at least one of the one or more flexible orstretchable LED arrays and at least one of the one or more flexible orstretchable PD arrays; wherein the second object receives at least aportion of the electromagnetic and thereby generates scattered, emittedor reflected electromagnetic radiation; and detecting at least a portionof the scattered, emitted or reflected electromagnetic radiation with atleast one of the one or more flexible or stretchable PD arrays.

In embodiments, the proximity sensor device further comprises one ormore inorganic semiconductor elements supported by the flexible orstretchable substrate. Optionally, the one or more inorganicsemiconductor elements are provided in an individually encapsulatedlayer, provided in a multilayer stacked geometry. In embodiments, theproximity sensor device further comprises a barrier layer encapsulatingat least a portion of the one or more flexible or stretchable LEDarrays, at least a portion of the one or more flexible or stretchable PDarrays, or at least portions of both the one or more flexible orstretchable LED array and the one or more flexible or stretchable PDarrays. In embodiments, the barrier layer comprises a bioresorbablematerial, a biocompatible material, or a combination of bioresorbableand biocompatible materials.

In embodiments, a flexible or stretchable LED array comprises one ormore individually encapsulated LED array layers provided in a multilayerstacked geometry, for example 2 to 1000 individually encapsulated LEDarray layers in a multilayer laminated geometry. In embodiments, aflexible or stretchable PD array comprises one or more individuallyencapsulated PD array layers provided in a multilayer stacked geometry,for example 2 to 1000 individually encapsulated PD array layers in amultilayer laminated geometry. In one embodiment, the one or moreflexible or stretchable LED arrays and the one or more flexible orstretchable PD arrays are provided in a multilayer laminated geometry.

In embodiments, each flexible or stretchable LED array comprises one ormore inorganic LEDs having an average thickness less than or equal to100 μm. In embodiments, each inorganic LED has one or more lateraldimensions selected over the range of 250 nm to 1000 μm. Optionally,each inorganic LED in a flexible or stretchable LED array isindependently selected from the group consisting of AlInGaP LEDs, GaNLEDs, stacked inorganic LEDs, inorganic LEDs incorporating a phosphorand any combination of these. Optionally, each LED independentlyproduces infrared electromagnetic radiation, visible electromagneticradiation, ultraviolet electromagnetic radiation, broadbandelectromagnetic radiation or narrowband electromagnetic radiation.Optionally, each LED independently produces electromagnetic radiationhaving a wavelength selected over the range of 100 nm to 5000 nm.

In embodiments, each flexible or stretchable PD array comprises one ormore inorganic semiconductor elements having an average thickness lessthan or equal to 100 μm. In embodiments, each inorganic semiconductorelement in a flexible PD array has one or more lateral dimensionsselected over the range of 250 nm to 1000 μm. In embodiments, eachflexible or stretchable PD array comprises one or more inorganic LEDsoperated in reverse bias mode. In embodiments, each flexible orstretchable PD array comprises one or more GaAs diode.

In one embodiment, the flexible or stretchable substrate of a proximitysensor device comprises a surgical glove. Optionally, the one or moreflexible or stretchable LED arrays and the one or more flexible orstretchable PD arrays are positioned on a fingertip region of thesurgical glove. In another embodiment, the flexible substrate comprisesa surgical instrument. In embodiments, a proximity sensor isincorporated into a robotic device for autonomous sensing of distancesbetween objects.

In embodiments, the one or more flexible or stretchable LED arrays andthe one or more flexible or stretchable PD arrays are positionedproximate to one another on the flexible or stretchable substrate. Inembodiments, the one or more flexible or stretchable LED arrays and theone or more flexible or stretchable PD arrays are positioned in physicalcontact with one another on the flexible or stretchable substrate. Inembodiments, the one or more flexible or stretchable LED arrays and theone or more flexible or stretchable PD arrays are positioned to overlapone another on the flexible or stretchable substrate. In otherembodiments, the one or more flexible or stretchable LED arrays and theone or more flexible or stretchable PD array are spatially separatedfrom one another on the flexible or stretchable substrate a distanceselected over the range of 10 nm to 10 mm, 100 nm to 1 mm or 1 μm to 100μm.

In certain embodiments, at least a portion of the one or more flexibleor stretchable LED arrays is positioned proximate to a neutralmechanical surface of the proximity sensor device. In embodiments, atleast a portion of the one or more flexible or stretchable PD arrays ispositioned proximate to a neutral mechanical surface of the proximitysensor device. Optionally, portions of the one or more LED arrays arepositioned at a distance selected over the range of 0 nm to 100 μm froma neutral mechanical plane of the proximity sensor device. Optionally,portions of the one or more PD arrays are positioned at a distanceselected over the range of 0 nm to 100 μm from a neutral mechanicalplane of the proximity sensor device.

In embodiments, one component of a multiple component integrated deviceis a flexible or stretchable electronic circuit. In embodiments,flexible or stretchable electronic circuits, such as flexible orstretchable LED arrays or flexible or stretchable PD arrays, are usefulwith the devices and methods described herein. One embodiment of aflexible or stretchable electronic circuit comprises a plurality ofinorganic semiconductor elements having an average thickness selectedover the range of 250 nm to 100 μm. Useful flexible or stretchableelectronic circuits include those comprising one or more singlecrystalline semiconductor elements. Optionally, inorganic semiconductorelements useful with the flexible or stretchable electronic circuits ofthe devices and methods described herein include semiconductornanoribbons, semiconductor membranes, semiconductor nanowires and anycombination of these. In embodiments, a flexible or stretchableelectronic circuit comprises a large area array.

In specific embodiments, a flexible or stretchable electronic circuituseful in the devices and methods described herein comprises one or moreflexible or stretchable single crystalline inorganic semiconductorelements. Useful flexible or stretchable semiconductor elements includethose having lateral dimensions selected over the range of 250 nm to100000 μm, optionally for some applications 1 μm to 10000 μm, andoptionally for some applications 10 μm to 1000 μm. Optionally, eachinorganic semiconductor element in a flexible or stretchable electroniccircuit has a net flexural rigidity less than or equal to 1×10⁻⁴ N·m.Optionally, each inorganic semiconductor element in a flexible orstretchable electronic circuit has a net bending stiffness less than orequal to 1×10⁸ GPa μm⁴.

Useful inorganic semiconductor elements include those selected from thegroup consisting of a transistor, a diode, an amplifier, a multiplexer,a light emitting diode, a laser, a temperature sensor (e.g.,thermistor), a heater (e.g., semiconductor resistive heater), aphotodiode, a photodetector, an integrated circuit, a sensor and anactuator. In an embodiment, the inorganic semiconductor elements of thedevice include one or more temperature sensors, such as a thermocouple,thermistor, silicon diode temperature sensor or platinum resistortemperature sensor. In an embodiment, the inorganic semiconductorelements of the device include one or more heaters, such as resistiveheaters. Use of a combination of a temperature sensor and heater isbeneficial in embodiments providing drug delivery functionality,including controlled release drug delivery. Optionally, an inorganic LEDelement of any device described herein can be substituted with aninorganic laser diode element. Useful laser diode elements include thosehaving an average thickness less than or equal to 100 μm. Optionally,the flexible or stretchable electronic circuits comprise one or moresemiconductor elements arranged to form an active circuit, for example,a circuit which performs one or more discrete functions, such anamplifier circuit or a multiplexing circuit.

In specific embodiments, flexible or stretchable electronic circuitsused with the devices and methods described herein comprise a pluralityof electronically interconnected island-bridge structures. In a specificembodiment, an island structure of an island-bridge structure comprisesa semiconductor circuit element. In a specific embodiment, a bridgestructure of an island-bridge structure comprises a flexible orstretchable electrical interconnection, such as an electricalinterconnection having a serpentine geometry.

In embodiments, a component of a multiple component integrated device isa flexible or stretchable LED array. In embodiments, a flexible orstretchable electronic circuit component of a multiple componentintegrated device is a flexible or stretchable LED array. In someembodiments, a multiple component integrated device comprises multipleflexible or stretchable LED arrays. In certain embodiments, a flexibleor stretchable electronic circuit useful for the devices and methodsdescribed herein comprise a flexible or stretchable array of lightemitting diodes (LEDs). In one embodiment, a flexible or stretchablearray of light emitting diodes comprises a plurality of light emittingdiodes in electrical communication with a plurality of stretchable orflexible electrical interconnects. In a specific embodiment, a flexibleor stretchable array of light emitting diodes is an island-bridgestructure, for example where an island structure comprises a lightemitting diode element and where a bridge structure comprises a flexibleor stretchable electrical interconnection. Certain embodiments provide adensity of light emitting diodes in a flexible or stretchable array oflight emitting diodes selected over the range of 1 LED mm⁻² to 1000 LEDsmm⁻². Useful light emitting diodes with the devices and methodsdescribed herein include, but are not limited to AlInGaP LEDs, GaN LEDs,stacked inorganic LEDs, inorganic LEDs incorporating a phosphor or anycombination of these. In embodiments, an ON/OFF state of an inorganicLED within the LED array is independent from ON/OFF states of otherinorganic LEDs within the array.

In embodiments, each LED in an array independently produceselectromagnetic radiation having a wavelength selected over the range of1000 nm to 5000 nm. In embodiments, each LED in the array independentlyproduces infrared electromagnetic radiation, visible electromagneticradiation, ultraviolet electromagnetic radiation, broadbandelectromagnetic radiation or narrowband electromagnetic radiation.Optionally, one or more LEDs in an array comprise stacked LEDs, forexample one or more LED elements in a stacked configuration. Inembodiments, a stacked LED comprises two or more LED elements that emitlight of two or more specific wavelengths or wavelength ranges. In aspecific embodiment, a stacked LED element comprises an LED that emitsred light, and LED that emits green light and an LED that emits bluelight, all provided in a stacked configuration. In another embodiment,multiple LED arrays are provided in a multilayer stacked geometry. Inone embodiment, a multilayer stacked LED array comprises a first layercomprising an array of LEDs that emit light of a first wavelength orwavelength range and a second layer comprising an array of LEDs thatemit light of a second wavelength or wavelength range. Additionalembodiments contemplated further comprise an additional layer comprisesan array of LEDs that emit light of an additional wavelength orwavelength range. In a specific embodiment, a first LED array in amultilayer stack emits red light, a second LED array in a multilayerstack emits green light and a third LED array in a multilayer stackemits blue light. Additional embodiments include LED arrays that emitwhite light or light of a broad wavelength range.

In embodiments, a flexible or stretchable LED array generates anintensity of electromagnetic radiation that is sufficient forvisualization, for actuating a tissue, for detection, for transmissionthrough a plasmonic crystal, for detection by a flexible or stretchablePD array, or sufficient for any combination of these.

In exemplary embodiments, a flexible or stretchable electronic circuitcomprises a multilayer structure. In embodiments, one or more flexibleor stretchable electronic circuits are provided in individuallyencapsulated layers in a multilayer stacked geometry. In a specificembodiment, a multilayer structure of this aspect comprises a pluralityof individually encapsulated LED array layers provided in multilayerlaminated geometries. In specific embodiments, multilayer structuresinclude those comprising 2 to 1000 individual layers. Flexible orstretchable electronic circuits comprising a multilayer structure areuseful, for example, for providing flexible or stretchable electroniccircuits exhibiting a variety of fill factors, such as fill factorsselected over the range of 1×10⁻⁶ to 1×10⁻³. In one embodiment,individually encapsulated LED array layers are provided in a laterallyoffset configuration; such a configuration is useful for providing fillfactors greater than 1×10⁻⁶. As used herein, the expression “laterallyoffset” refers to a multilayer geometry wherein at least a portion ofthe LEDs in different layers of the device are positioned such that theydo not reside on top of each other. As used in this context, the term“fill factor” refers to the fraction of the area of the footprint of thedevice that is occupied by the LED structures. In certain embodiments,adhesives or adhesive layers are provided between individual layers of amultilayer structure to unite the components a single multilayer device.Optionally, an individual layer in a multilayer structure has aninternal adhesive layer. In certain embodiments, the individual layersof a multilayer structure are each provided on individual substrateswith an adhesive layer provided between the substrates to unite theindividual layers into a single multilayer device. In certainembodiments, the individual layers are encapsulated to unite the layersinto a single multilayer device. In certain embodiments, one layer islaminated on top of another layer to unite the layers into a singlemultilayer device.

In certain embodiments, a flexible or stretchable electronic circuitsupported by an external surface of a suture or a flexible orstretchable substrate covers a percentage of the external surface of thesuture or the flexible or stretchable substrate, for example apercentage selected over the range of 1% to 100%, optionally for someapplications selected over the range of 10% to 100%, optionally for someembodiments selected over the range of 10% to 60% and optionally forsome applications selected over the range of 40% to 100%. In certainembodiments, a flexible or stretchable electronic circuit supported byan external surface of a suture or a flexible or stretchable substratecovers a percentage of the external surface of the suture or theflexible or stretchable substrate, for example a percentage that is 10%or more, optionally for some embodiments 20% or more, and optionally forsome embodiments 40% or more. In specific embodiments, a flexible orstretchable electronic circuit covers an area of the external surface ofa suture selected over the range of 1 mm² to 10,000 mm², selected overthe range of 100 mm² to 1000 mm², greater than or equal to 100 mm² orgreater than or equal to 1 mm². In an embodiment, a flexible orstretchable electronic circuit is a large area device.

For some embodiments, a flexible or stretchable electronic circuit ispositioned proximate to a neutral mechanical surface of a device. Insome embodiment, a thickness of a barrier layer and a thickness of asubstrate are selected so as to position one or more semiconductorcircuit elements in a flexible or stretchable electronic circuitproximate to a neutral mechanical surface of a device.

Optionally, a flexible or stretchable electronic circuit is assembledvia transfer printing, for example via dry transfer contact printing.U.S. Pat. No. 7,557,367 describes useful transfer printing methods. Arange of transfer printing methods are useful for assembly of a flexibleor stretchable electronic circuit, including those using a conformabletransfer device. In an embodiment, a step of assembling a flexible orstretchable electronic circuit comprises the steps of: contacting one ormore contact surfaces of semiconductor components and/or electrodes witha transfer surface of a conformable transfer device, thereby generatinga conformable transfer device having the semiconductor components and/orelectrodes disposed on a transfer surface; contacting the transfersurface of the conformable transfer device having the semiconductorcomponents and/or electrodes with the receiving surface of a flexible orstretchable substrate in a manner to establish conformal contact betweenthe transfer surface of the conformal transfer device and the receivingsurface of the flexible or stretchable substrate; and separating theconformable transfer device and the semiconductor components and/orelectrodes, thereby transferring the semiconductor components and/orelectrodes to the receiving surface of the flexible or stretchablesubstrate. In an embodiment, the semiconductor components and/orelectrodes are at least partially encapsulated by a barrier layer andthe transfer surface of the conformable transfer device contacts thebarrier layer provided on the contact surfaces of the semiconductorcomponents or electrodes. In an embodiment, the conformal transferdevice is a stamp, such as an elastomer stamp or a composite elastomerstamp.

A specific method of making a flexible or stretchable electronic devicecomprises the steps of providing a substrate having a sacrificial layer;applying a first dielectric layer on the sacrificial layer of thesubstrate; providing one or more inorganic semiconductor components onthe first dielectric layer; covering a portion of the one or moreinorganic semiconductor components with a second dielectric layer,thereby generating a covered inorganic semiconductor component having anexposed distal end; providing an electrode that physically contacts theexposed distal end of an inorganic semiconductor component; removing atleast a portion of the first dielectric layer, the second dielectriclayer or both, thereby generating a mesh structure; removing thesacrificial layer on the substrate to leave a mesh structure; andtransferring the mesh structure to a receiving surface of a flexible orstretchable substrate. In an embodiment, the step of removing at least aportion of the first dielectric layer and the second dielectric layer togenerate the mesh structure comprises etching, for example, oxygenreactive ion etching. In an embodiment, the step of providing one ormore inorganic semiconductor components on the first dielectric layer iscarried out via transfer printing, for example, via dry contact transferprinting. In an embodiment, the step of transferring the mesh structureto a receiving surface of a flexible or stretchable substrate is carriedout via transfer printing, for example, via dry contact transferprinting.

In some embodiments, the geometry of electronic devices may be used toprovide stretchability, flexibility, conformability and/orcompressibility. In an embodiment, the devices may exploit inorganicsemiconductor materials configured into structural shapes that cangeometrically accommodate large mechanical deformations withoutimparting significant strain in the materials themselves. For example,bridges connecting rigid device islands may be wavy, buckled, serpentineor meandering as further described in U.S. Patent ApplicationPublication Nos. US 2008/0157235 and US 2010/059863. In an aspect,devices disclosed herein comprise one or more stretchable components,such as disclosed in U.S. Patent Application Publication Nos. US2008/0157235, US 2010/059863 and US 2010/0002402, and are made by one ormore of the processes disclosed therein. U.S. Patent ApplicationPublication Nos. US 2008/0157235, US 2010/059863 and US 2010/0002402 arehereby incorporated by reference in their entireties to the extent notinconsistent herewith.

In embodiments, one component of a multiple component integrated deviceis a barrier layer, for example a barrier layer comprising a polymer orelastomer. In exemplary embodiments, barrier layers used in the devicesand methods described herein prevent water from a biological environmentor a non-biological environment from contacting at least a portion of aflexible or stretchable electronic circuit or components thereof. Forexample, a barrier layer of one embodiment provides a net permeabilitywith respect to transport of water low enough to prevent an electricalshort circuit in a flexible or stretchable electronic circuit. Usefulbarrier layers include, but are not limited to barrier layers whichlimit a leakage current between a biological environment and a flexibleor stretchable electronic circuit or a component thereof, barrier layerswhich limit a temperature difference between a biological environmentand a flexible or stretchable electronic circuit or a component thereof,barrier layers which selectively permit transmission of electromagneticradiation between a biological environment and a flexible or stretchableelectronic circuit or a component thereof, barrier layers whichselectively permit transport of one or more compositions to or from abiological environment, and any combination of these.

In a specific embodiment, a barrier layer provides or limits a netleakage current from a flexible or stretchable electronic to 10 μA orless, and for some applications 0.01 pA/cm² or less, and for someapplications 0.001 μA/cm² or less. In some embodiments, a barrier layerhas an electrical resistivity of 10¹⁴ Ω·m or greater, for example anelectrical resistivity selected over the range of 10¹⁵ to 10¹⁷ Ω·m. Insome embodiments, the barrier layer prevents the rate at which charge isleaked from the electronic device; for example, one barrier layerembodiment limits electrical discharge from a device to 10 μC or lessover a period of 1 second. In some embodiments, the barrier layer limitsleakage current or average leakage current from the device to 10 μA orless or 5 μA or less over a long period of time, such as 3 hours or moreor 5 hours or more.

Barrier layers which selectively permit transmission of electromagneticradiation include those having at least portions which are opticallytransparent and those having at least portions which are opticallyopaque. Certain barrier layers include at least portions which havespecific wavelength regions which are at least partially transparent,such as wavelength regions selected over the range of 100 nm to 300 μmor any sub-range therein. Useful barrier layers further include thoselayers in which the transmission properties are modulated by anelectronic circuit in contact with the barrier layer or a componentthereof.

Barrier layers which selectively permit transport of one or morecompositions to or from a biological environment include those having atleast portions which have an increased permeability for one or morecompositions. Barrier layers of this class are useful, for example forpermitting introduction of one or more pharmaceutical compositions to abiological environment from within the barrier layer or from anelectronic circuit in contact with the barrier layer. In someembodiments, the permeability of portions of a barrier layer ismodulated by an electronic circuit or a component thereof in contactwith the barrier layer.

In specific embodiments, a barrier layer has an average thickness over aflexible or stretchable electronic circuit less than or equal to 1000μm, optionally for some embodiments less than or equal to 100 μm andoptionally for some embodiments less than or equal to 10 μm. Optionally,a barrier layer has a thickness over at least a portion of a flexible orstretchable electronic circuit selected over the range of 250 nm to 1000μm, optionally for some embodiments selected over the range of 1 μm to500 μm, and optionally for some embodiments selected over the range of10 μm to 100 μm. In some embodiments, a barrier layer comprises aplurality of individual layers, for example where each layer has athickness selected over the range of 250 nm to 1000 μm and/or where thetotal thickness of the multiple layers is less than or equal to 1000 μm.In embodiments, a barrier layer is a stretchable or flexible layer. Inembodiments, a barrier layer has an average modulus selected over therange of 0.5 kPa to 10 GPa, optionally for some application selectedover the range of 1 KPa to 1 GPa, optionally for some applicationselected over the range of 1 KPa to 100 MPa, optionally for someapplication selected over the range of 1 KPa to 1 MPa. As will begenerally understood by one skilled in the art, use of a barrier layerwith a relatively high modulus (e.g., greater than 1 GPa) in someembodiments may require a small thickness (e.g., less than 100 μm oroptionally less than 10 μm) to provide net device mechanical properties(e.g., bending stiffness or flexural rigidity) useful for sometherapeutic and diagnostic applications. In embodiments, a barrier layerhas net flexural rigidity less than or equal to 1×10⁻⁴ Nm. Inembodiments, a barrier layer has a net bending stiffness less than orequal to 1×10⁸ GPa μm⁴, optionally for some applications less than orequal to 1×10⁷ GPa μm⁴, and optionally for some applications less thanor equal to 1×10⁶ GPa μm⁴.

Optionally, barrier layers useful with the devices and methods describedherein comprise a biocompatible material, a bioinert material or acombination of biocompatible and bioinert materials. In one embodiment,a barrier layer comprises a bioresorbable material. Useful barrierlayers include those comprising a material selected from the groupconsisting of a polymer, an inorganic polymer, an organic polymer, anelastomer, a biopolymer, a ceramic and any combination of these.Specific barrier layers include those comprising PDMS, polyimide, SU-8,parylene, parylene C, silicon carbide (SiC), or Si₃N₄. Optionally,barrier layers useful with the devices and methods described hereininclude barrier layers which are microstructured or nanostructuredlayers having one or more microstructured or nanostructured openings,channels, vias, receiving surfaces, relief features, opticallytransmissive regions, optically opaque regions or selectively permeableregions that are permeable to one or more target molecules. Optionally,an adhesive layer is provided adjacent to a barrier layer, for example aPDMS layer.

Optionally, a barrier layer may completely or partially encapsulateinorganic semiconductor components or electrodes of a flexible orstretchable electronic device. In an embodiment, the barrier layercomprises a mesh structure. Such a mesh structure may be formed, forexample, by removing material from selected regions of the barrierlayer, for example, via wet or dry etching (e.g., reactive oxygenetching).

Optionally, devices described herein further comprise one or morepharmaceutical compositions, for example pharmaceutical compositions atleast partially encapsulated by a barrier layer or pharmaceuticalcompositions incorporated into the barrier layer material. The term“pharmaceutical composition” is used herein interchangeably with theterm “drug.” Useful pharmaceutical compositions include, but are notlimited to antibiotics, antiseptics, proteins, nucleic acids,anti-inflammatories, carbohydrates, analgesics, antipyretics,anti-fungals, antihistamines, hormones, antivirals, vitamins,antibodies, photosensitizers and any combination of these. In a specificembodiment, the barrier layer comprises a bioresorbable material and thedevice further comprises one or more pharmaceutical compositions. Inthese embodiments, when the bioresorbable material is at least partiallyresorbed or dissolved by a biological environment, at least a portion ofa pharmaceutical composition is released into the biologicalenvironment.

Optionally, when a device comprises a pharmaceutical composition, theflexible or stretchable electronic circuit comprises a thermal,electrical or optical actuator, such that a portion of thepharmaceutical composition is released to the biological environmentupon actuation of the flexible or stretchable electronic circuit. Inembodiments, actuation of a flexible or stretchable electronic circuitthermally, optically, or electrically actuates the barrier layer suchthat the pharmaceutical composition is released. In embodiments,actuation of a flexible or stretchable electronic circuit changes apermeability of at least a portion of the barrier layer, permittingrelease of a portion of the pharmaceutical composition to a biologicalenvironment. In embodiments, actuation of a flexible or stretchableelectronic circuit melts, photolytically degrades or otherwise rendersporous at least a portion of the barrier layer, thereby releasing atleast a portion of the pharmaceutical composition to a biologicalenvironment. In certain embodiments, when a pharmaceutical compositionis released to a biological environment it is exposed to electromagneticradiation generated by a flexible or stretchable electronic circuit tophotoactivate the pharmaceutical composition. In certain embodiments,heating of a barrier layer by actuation of a flexible or stretchableelectronic circuit partially degrades the barrier layer to releaseportions of a pharmaceutical composition contained therein.

In embodiments, components of a multiple component integrated device areoptical elements. For example, in certain embodiments, devices describedherein further comprise one or more optical elements. Optical elementsuseful in the devices and methods described herein include coatings,reflectors, windows, optical filters, collecting optics, diffusingoptics, concentrating optics and combinations of these. In embodiments,optical elements comprise molded structures. In embodiments, the opticalelements are positioned in optical communication with other devicecomponents, for example a flexible or stretchable electronic circuit, aflexible or stretchable LED array, a flexible or stretchable PD array, aflexible or stretchable substrate, a detector, a plasmonic crystal andany combination of these. In certain embodiments, an optical elementcomprises a molded structure, such as a replica molded structure. Inembodiments, an optical element comprises a lithographically patternedstructure, for example patterned by a conventional lithographic methodknown in the art of microfabrication. In a specific embodiment, anoptical element comprises a structure patterned by nano-imprintlithography. In one embodiment, a method of making an optical elementcomprises the steps of providing a prepolymer layer, molding orpatterning the prepolymer layer and curing the prepolymer layer. Usefuloptical elements include those provided in optical communication withone or more semiconductor device elements, for example LEDs or PDs.

In another aspect, a multiple component integrated device is a fluiddelivery monitor. Fluid delivery monitors are useful, for example, inmethods for monitoring flowing fluids. A device of this aspect comprisesa tube for delivery of a fluid, a flexible or stretchable plasmoniccrystal device conformally positioned on a surface of the tube, and adetector positioned in optical communication with the plasmonic crystaldevice to receive electromagnetic radiation. In one embodiment, the tubeaccommodates the plasmonic crystal device. In one embodiment, the tubeand plasmonic crystal device comprise a unitary structure. In oneembodiment, the plasmonic crystal device is provided in an aperture inthe tube, for example such that a sensing surface of a plasmonic crystalis provided in physical contact with a fluid in the tube. In anembodiment, the flexible or stretchable plasmonic crystal device isfabricated into the tube.

A method of this aspect for monitoring a fluid flowing in a tubecomprises the steps of flowing the fluid through the tube, providing aflexible or stretchable plasmonic crystal device conformally on asurface of the tube, passing electromagnetic radiation from theplasmonic crystal device through the flowing fluid and detecting atleast a portion of the electromagnetic radiation which passes throughthe flowing fluid with a detector.

In specific embodiments, the flexible or stretchable plasmonic crystaldevice comprises a flexible or stretchable light emitting diode (LED)array supported by a first flexible or stretchable substrate and aplasmonic crystal positioned in optical communication with the flexibleor stretchable LED array. Optionally the plasmonic crystal is supportedby a separate substrate, for example a substrate positioned between aplasmonic crystal and a flexible or stretchable LED array. Optionally,the device may further comprise one or more inorganic semiconductorelements supported by the first flexible substrate, for example inindividually encapsulated layers provided in a multilayer stackedgeometry. In a specific embodiment, the plasmonic crystal is positionedin optical communication with a detector. In a specific embodiment, theplasmonic crystal is provided in physical contact with the fluid beingmonitored. In a specific embodiment, a sensing surface of the plasmoniccrystal is provided in physical contact with the fluid.

In embodiments, the flexible or stretchable LED array produceselectromagnetic radiation and the plasmonic crystal receives at least aportion of the electromagnetic radiation and transmits at least aportion of the electromagnetic radiation to produce transmittedelectromagnetic radiation. In these embodiments, the detector receivesand detects at least a portion of the transmitted electromagneticradiation. Optionally, the detector detects an intensity of thetransmitted electromagnetic radiation, for example, as a function oftime, as a function of wavelength, or as a function of position, forexample as a function of the position of the plasmonic crystal that theelectromagnetic radiation is transmitted through. In some embodiments, aproperty of the flowing fluid is determined from the detected intensity.For example, useful properties determined from the detected intensityinclude, but is not limited to, a refractive index of the fluid, acomposition of the fluid, a presence or absence of a pharmaceuticalcomposition in the fluid, a concentration of a pharmaceuticalcomposition in the fluid, a density of the fluid, a flow rate of thefluid and any combination of these.

In embodiments, the flexible or stretchable LED array comprises aplurality of inorganic LEDs having a thickness less than or equal to 100μm. Optionally each individual inorganic LED in the flexible orstretchable LED array has one or more lateral dimensions selected overthe range of 250 nm to 1000 μm. In embodiments, the inorganic LEDS areAlInGaP LEDs, GaN LEDs, stacked inorganic LEDs, inorganic LEDsincorporating a phosphor or any combination of these. In embodiments, anON/OFF state of an inorganic LED within the LED array is independentfrom ON/OFF states of other inorganic LEDs within the array. Inembodiments, each LED in the array independently produceselectromagnetic radiation having a wavelength selected over the range of1000 nm to 5000 nm. In embodiments, each LED in the array independentlyproduces infrared electromagnetic radiation, visible electromagneticradiation, ultraviolet electromagnetic radiation, broadbandelectromagnetic radiation or narrowband electromagnetic radiation.

Optionally the flexible or stretchable LED array comprises anencapsulation layer provided over the individual inorganic LEDs in thearray, such as an encapsulation layer which prevents fluid from makingdirect contact with the LEDs. The flexible or stretchable LED array mayoptionally comprise a plurality of individually encapsulated LED arraylayers provided in a multilayer stacked geometry. In a specificembodiment, the flexible or stretchable LED array comprises 2 to 1,000individually encapsulated LED array layers provided in a multilayerlaminated geometry. Optionally, the LED array is assembled by transferprinting. In a specific embodiment, the LED array is an island-bridgestructure, for example where islands of the island-bridge structure areprovided by a plurality of inorganic LEDs and bridges of theisland-bridge structure are provided by a plurality of flexibleelectrical interconnects positioned in electrical communication with theplurality of inorganic LEDs. In one embodiment, a plasmonic crystalcomprises a molded or embossed structure on a flexible or stretchableLED array, for example a molded or embossed encapsulation layer. In aspecific embodiment, a plasmonic crystal and a flexible or stretchableLED array of a flexible or stretchable plasmonic crystal device areprovided in a multilayer laminated geometry.

Useful plasmonic crystals include those fabricated by replica moldingmethods or nano-imprint lithography methods. U.S. Pat. No. 7,705,280further discloses plasmonic crystals useful with the methods and devicesdescribed herein. Optionally, the plasmonic crystal is assembled bytransfer printing. In a specific embodiment, the plasmonic crystal is inphysical contact with the flowing fluid. In one embodiment, the secondflexible or stretchable substrate and the plasmonic crystal comprise aunitary structure. Optionally, the photonic crystal comprises thesubstrate having a nanoimprinted or replica-molded structure.

In embodiments, the tube for flowing the fluid is flexible orstretchable. Optionally the tube has a circular cross section.Optionally the tube has a non-circular cross section, such as arectangular cross section or polygonal cross section. In embodiments,the tube has an outer diameter selected over the range of 100 μm to 10mm. In embodiments, the tube has an inner diameter selected over therange of 100 μm to 10 mm. Optionally the tube has a nanostructured orpatterned surface, for example for accommodating the flexible LED arrayor a component thereof or the plasmonic crystal. In one embodiment, theplasmonic crystal is molded into the tube, for example by replicamolding or nano-imprint lithography. Optionally the plasmonic crystalcomprises a nanostructured or microstructured surface of the tube andthe tube comprises the second flexible or stretchable substrate. In oneembodiment, the tube is positioned in fluid communication with a patientor subject, for example such that the fluid is delivered to or withdrawnfrom the patient or subject. Optionally, the fluid flowing through thetube is fluid for intravenous delivery. Optionally, the tube is anintravenous delivery tube. In one embodiment, the tube comprises abiocompatible material. Optionally the tube has a non-circular crosssection. In embodiments, the tube has an outer lateral dimensionselected over the range of 100 μm to 10 mm. In embodiments, the tube hasan inner lateral dimension selected over the range of 100 μm to 10 mm.In specific embodiments, the tube is at least partially transparent toelectromagnetic radiation having a wavelength or wavelength distributionselected over 100 nm to 5000 nm.

In a specific embodiment, a plasmonic crystal comprises a substratehaving a first surface with a plurality of features provided in a firstarray, where the substrate comprises a dielectric material; and one ormore films comprising an electrically conductive material, wherein atleast a portion of the one or more films is supported by the firstsurface, and wherein at least a portion of the one or more filmscomprising the electrically conducting material is spatially alignedwith each of the features of the first surface; wherein the spatialdistribution, physical dimensions or both of the features of the firstarray are selected such that at least a portion of electromagneticradiation incident to the plasmonic crystal excites plasmonic responsesin the one or more films comprising the electrically conductingmaterial. In embodiments, the electrically conducting material ispositioned in physical contact with the fluid. In embodiments, thedielectric material receives electromagnetic radiation produced by theflexible or stretchable array of LEDs.

Features of the first array of the first surface of the substrate usefulin the described embodiments include apertures, recessed features,relief features or any combination of these. In an embodiment, forexample, features of the first array comprise apertures extendingthrough the entire thickness of the substrate, and optionally comprise ananohole array. In other embodiments, features of the first arraycomprise relief features extending from the substrate, including but notlimited to, arrays of cubes, columns, ribbons, posts and prisms or anycombination of these relief features. In other embodiments, features ofthe first array comprise recessed features extending into the substrateincluding, but not limited to, depressions, channels, grooves, bores,openings, slits or any combination of these.

Optionally, the substrate of such a plasmonic crystal comprises apolymer material. Optionally, the substrate comprises a nanoimprintedstructure or a replica-molded structure. Optionally, the plasmoniccrystal comprises a three dimensional plasmonic crystal. Optionally, theone or more films comprising the electrically conducting materialcomprise a metallic or semiconducting optical grating structure.Optionally, the one or more films comprising an electrically conductingmaterial comprise one or more metal or semiconductor films havingthicknesses selected from the range of about 5 nm to about 5 μm.Optionally, a portion of the one or more films of the electricallyconductive material have the same cross sectional shapes as at least aportion of the features of the first array.

In embodiments, the features of a first array in the above describedplasmonic crystal are selected from the group consisting of: aperturesextending entirely through the substrate; relief features extending fromthe substrate; and recessed features extending into the substrate.Optionally at least a portion of features of a first array of aplasmonic crystal are nanosized features or nanostructured features. Forexample, in some embodiments, the features extend heights into thesubstrate or extend heights away from the substrate selected from therange of 5 nm to 5 μm. In specific embodiments, the features of havecross sectional shapes selected from the group consisting of circular,square, rectangular, trapezoidal, ellipsoid, triangular or anycombination of these. Optionally, the features of have submicron crosssectional dimensions. In a specific embodiment, the features areprovided in a periodic array. Optionally, the periodic array furthercomprises at least one defect.

In embodiments, the features of the first array are recessed features,relief features, apertures or any combination of these, wherein one ormore films comprising the electrically conductive material comprises acontinuous or discontinuous film supported by the first surface andcovering at least a portion of the features provided in the first array.Optionally, the continuous film is a unitary film. In one embodiment,the continuous or discontinuous film is provided in physical contactwith the first surface. In one embodiment, the continuous ordiscontinuous film is provided in conformal contact with the firstsurface. In an embodiment, each of the features have side surfaces and atop surface or a bottom surface; wherein the continuous film covers theside surfaces and the top surface or the bottom surface of at least aportion of the features.

In some embodiments, a plasmonic crystal further comprises an additionalsubstrate in contact with the substrate having the first surface,wherein at least a portion of the features of the first array areapertures extending through the substrate having the first surface,wherein the additional substrate is positioned such that the aperturesin the substrate having the first surface expose exposed regions of theadditional substrate, and wherein the continuous film covers at least aportion of the exposed regions of the additional substrate.

In specific embodiments, the one or more films comprise: a first filmsupported by a portion of the first surface, and a plurality of filmsprovided in a second array, wherein at least one of the films of thesecond array is spatially aligned with each of the features of the firstsurface; and wherein at least a portion of the films of the second arrayare physically displaced from the first film. Optionally, the first filmis provided in a first layer and the films of the second array areprovided in a second layer, wherein the plasmonic crystal has amultilayered geometry. In an embodiment the first layer having the firstfilm is separated from the second layer having the array of second filmsby distances selected over the range of about 5 nm to about 5 μm.

In embodiments, the first array of features comprises an array ofrecessed features having bottom surfaces or relief features having topsurfaces; wherein at least a portion of the films of the second arrayare positioned on the bottom surfaces or the top surface of thefeatures. In embodiments, the first array of features comprises recessedfeatures, relief features or apertures having side surfaces, wherein theone or more films comprising the electrically conducting materialfurther comprise films covering a portion of the side surfaces of thefeatures.

Without wishing to be bound by any particular theory, there can bediscussion herein of beliefs or understandings of underlying principlesrelating to the invention. It is recognized that regardless of theultimate correctness of any mechanistic explanation or hypothesis, anembodiment of the invention can nonetheless be operative and useful.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A provides a side plan view of a biomedical device comprising asuture-mounted stretchable or flexible electronic circuit.

FIG. 1B provides a side plan view of a biomedical device comprising asuture-mounted proximity sensor device having a flexible or stretchableLED array and a flexible or stretchable PD array.

FIG. 1C provides a side plan view of a biomedical device comprising asuture-mounted drug delivery device having a temperature sensor, aheater, and a drug-containing region.

FIG. 1D provides a side plan view of a biomedical device comprising asuture-mounted drug delivery device having a temperature sensor, aheater, and a drug-containing region.

FIG. 1E provides a side plan view of a biomedical device comprising asuture-mounted drug delivery device having an optional photodetectorarray, an LED array, and a drug-containing region.

FIG. 1F provides a side plan view of a biomedical device comprising asuture-mounted drug delivery device having an optional photodetectorarray, an LED array, and a drug-containing region

FIG. 2 provides a top plan view of a biomedical device comprising asuture-mounted stretchable or flexible electronic circuit closing awound in a tissue.

FIG. 3 provides a top plan view of a portion of a biomedical devicecomprising a suture-mounted stretchable or flexible electronic circuit.

FIGS. 4A, 4B, 4C, 4D, and 4E provide a schematic showing variousapproaches for creating layers of flexible or stretchable electroniccircuits. FIG. 4A provides a side plan view of a flexible or stretchableelectronic circuit comprising an array of electronically interconnectedisland and bridge structures. FIGS. 4B, 4C, 4D, and 4E provide side planviews of stacked configurations of stretchable or flexible electroniccircuits wherein the layers are connected by an adhesive (FIG. 4B),directly connected (FIG. 4C), connected by a substrate (FIG. 4D), andconnected by substrates and adhesive (FIG. 4E).

FIGS. 4F, 4G, and 4H provide a schematic showing various approaches forcreating layers of flexible or stretchable electronic circuits. FIGS.4F, 4G, and 4H provide side plan views of stacked configurations ofstretchable or flexible electronic circuits wherein the layers areconnected by encapsulation (FIG. 4F), lamination (FIG. 4G), and printingon a laminated layer (FIG. 4H).

FIGS. 4I, 4J, 4K, 4L, 4M, 4N, 4O, 4P, 4Q, 4R, 4S, 4T, and 4U provideschematic diagrams of strategies to create optical elements on alaminated flexible or stretchable electronic circuit, including lenses(FIGS. 4I, 4J, 4K), diffusers (FIGS. 4L, 4M,4N), a reflective coating(FIGS. 4O-4P), a reflective coating having a transparent section (FIGS.4Q-4R), and a grating (FIGS. 4S, 4T, 4U).

FIG. 5A provides a side plan view of offset and stacked arrays offlexible or stretchable electronic circuits and FIG. 5B provides a topplan view of the same offset and stacked arrays of flexible orstretchable electronic circuits.

FIG. 6 provides a side plan view of a fluid delivery monitor devicecomprising a flexible or stretchable electronic circuit.

FIG. 7 provides a side plan view of a proximity sensor device comprisinga flexible or stretchable LED array and a flexible or stretchable PDarray.

FIG. 8 provides a flow diagram of a method employing a biomedical devicecomprising a suture having a flexible or stretchable LED array forexposing a wound to electromagnetic radiation.

FIG. 9 provides a flow diagram of methods of making a biomedical device.

FIG. 10 provides a flow diagram of a method of treating a tissue in abiological environment.

FIG. 11A provides an optical image of an array of μ-ILEDs (left) and aschematic illustration (right) and corresponding photograph (inset) of asingle μ-ILED element. FIG. 11B provides optical images of a stretchablearray of μ-ILEDs. FIG. 11C provides data showing current-voltage (I-V)characteristics of a μ-ILED array under different strain configurations(left) and voltage at 20 μA current for different cycles of stretching(right). FIG. 11D provides optical images of a stretchable array ofμ-ILEDs on a thin PDMS membrane in a flat configuration (top) and in ahemispherical, balloon state (bottom) induced by pneumatic pressure.FIG. 11E provides a magnified view of FIG. 11D from the top. FIG. 11Fprovides data showing I-V characteristics of the array in its flat andinflated state. FIG. 11G provides data showing 3D-FEM results.

FIG. 12A provides optical images of an array of μ-ILEDs on a band ofPDMS twisted to different angles, collected with (left) and without(right) external illumination. FIG. 12B provides an SEM image of thearray when twisted to 360°. FIG. 12C provides data showing I-Vcharacteristics of the array twisted by various amounts. FIG. 12Cprovides data showing 3D-FEM modeling results. FIG. 12D shows axialstrain, width strain, and shear strain. FIG. 12E provides optical imagesof an array of p-ILEDs stretched on the sharp tip of a pencil, collectedwith (left) and without (right) external illumination. The white arrowsindicate the direction of stretching. FIG. 12F provides optical imagesof a stretchable μ-ILED array wrapped and stretched downward on the headof a cotton swab; the inset image was obtained without externalillumination. FIG. 12G provides data showing I-V characteristics of thearray in FIG. 12E, before (initial), during (deformed) and after(released) deformation; the inset provides a graph of the voltage neededto generate a current of 20 μA, measured after different numbers ofcycles of deformation.

FIG. 13A provides a schematic, exploded view illustration for a stackeddevice formed by multilayer lamination. FIG. 13B provides optical imagesof a four layer stack of μ-ILEDs. FIG. 13C provides optical images of atwo layer stack of μ-ILEDs. FIG. 13D provides an optical image of anarray of μ-ILEDs on a piece of paper, in a folded state; the inset showsthe device in its flat state. FIG. 13E provides an optical image of anarray of μ-ILEDs on a sheet of aluminum foil in a crumpled state; theinset shows the device in its flat state. FIG. 13F provides opticalimages of an array of μ-ILEDs on a catheter balloon in its inflated(inset) and deflated states. FIG. 13G provides optical images of anarray of μ-ILEDs on a rigid plastic tube; the inset shows a magnifiedview of a single ILED. FIG. 13H provides an optical image of an isolatedμ-ILED with straight interconnects wrapped around a glass tube; theinset provides a magnified view. FIG. 13I provides an optical image ofan array of μ-ILEDs on a fiber, wrapped around a glass tube; the insetshows an image of an array of μ-ILEDs on a fiber in a knotted state.

FIG. 14A provides optical images of a light emitting suture in an animalmodel with a conventional suture needle. FIG. 14B provides a schematicexploded view illustration of an array of μ-ILEDs on a thin film coatedwith an adhesive. FIG. 14C provides an optical image of an animal modelwith a μ-ILED array implanted under the skin and on top of the muscletissue; the inset shows the device before implantation.

FIG. 15A provides a schematic illustration of a flexible plasmoniccrystal device. FIG. 15B shows an optical image of a thin, moldedplasmonic crystal on a plastic substrate wrapped around a cylindricalsupport. FIG. 15C provides an atomic force microscope image of thesurface of a plasmonic crystal. FIG. 15D provides data showingtransmission spectra collected over a range of wavelengths relevant forillumination of a plasmonic crystal by μ-LEDs. FIG. 15E provides anoptical image of a sensor integrated on a flexible tube, next to the tipof a pen; the inset shows the backside of a plasmonic crystal beforeintegration of μ-ILEDs. FIG. 15F provides optical images of a flexibleplasmonic crystal device with different fluids in the tube. FIG. 15Gprovides data showing measurement results from a sensor (top), as asequence of fluids pass through; the bottom frame shows the percentageincrease in light transmitted from the μ-ILED through the plasmoniccrystal.

FIG. 16A provides a schematic illustration of a stretchable opticalproximity sensor based on an array of μ-ILEDs and μ-IPDs. FIG. 16Bprovides an optical image of a stretchable optical proximity sensormounted on the fingertip region of a vinyl glove. FIG. 16C provides anoptical image of an array of μ-ILEDs transfer-printed on the fingertipregion of a vinyl glove; the inset shows a plot of photocurrent as afunction of distance between the sensor and an object. FIG. 16D provideoptical images of a stretchable optical proximity sensor mounted on thefingertip region of a vinyl glove before (left) and after (right)immersion into soapy water. FIG. 16E provides data showing I-Vcharacteristics of a μ-ILED array after operation in saline solution fordifferent immersion times.

FIG. 17A provides a schematic illustration and composition of a μ-ILEDelement. FIG. 17B provides a schematic illustration showing fabricationprocesses for μ-ILEDs arrays on a carrier glass substrate.

FIGS. 18A, 18B and 18C provide schematic illustrations (left frames) andcorresponding microscope images (top right frames) and SEM images(bottom right frames) of devices during transfer printing.

FIG. 19A provides a schematic illustration of a flexible device. FIG.19B provides a schematic illustration of the cross sectional structureat an island; the inset shows an SEM image of a μ-ILEDs array aftertransfer printing to a thin PDMS substrate. FIG. 19C provides aschematic illustration of the cross sectional structure at metalinterconnection bridges.

FIG. 20A provides SEM images of adjacent μ-ILEDs before (left) and after(right) stretching along the horizontal direction. FIG. 20B providesdata showing strain distributions determined by 3D-FEM.

FIGS. 21A and 21B provide optical microscope images of two pixels in aμ-ILED array with a serpentine bridge design before (left frame) andafter (right frame) external stretching along the horizontal direction.FIG. 21C provides data showing the results of a FEM simulation.

FIG. 22 provides optical images of a 6×6 μ-ILED array.

FIGS. 23A and 23B provide optical images of an 8×8 μ-ILED array on athin PDMS substrate. FIG. 23C provides data showing the results of a FEMcalculation.

FIG. 24A provides schematic illustrations of a 3×8 μ-ILED arrayintegrated on a thin PDMS substrate; the inset represents an opticalmicroscope image of this μ-ILED array on a handle glass substrate beforetransfer printing. FIG. 24B shows a magnified view of the SEM image inFIG. 12B. FIG. 24C provides data showing voltage at 20 μA current foreach twisting cycle of 360° during a fatigue test.

FIG. 25 provides data showing the results of FEM strain contours ofaxial (top), width (center), and shear (bottom) strains for 360° twistedPDMS substrate.

FIG. 26A provides data showing I-V characteristics of a 6×6 μ-ILED arrayas a function of deformation cycles. FIG. 26B provides data showingvoltage needed to generate a current of 20 μA during a fatigue test.

FIG. 27A provides a schematic illustration of stacked devices. FIG. 27Bprovides optical images of stacked devices collected without externalillumination.

FIG. 28A provides data showing the strain distribution of a two-layersystem in a stacked array bent to a radius of curvature 2 mm. FIG. 28Bprovides data showing the strain distribution in layers of a μ-ILEDisland.

FIG. 29A provides an optical image of a 6×6 μ-ILED array integrated onfabric in its bent and on state; the inset shows the device in its flatand off state. FIG. 29B provides data showing I-V characteristics ofthis array in its bent state; the inset provides a graph of the voltageneeded to generate a current of 20 μA during a fatigue test. FIG. 29Cprovides and optical image of an 8×8 μ-ILED array integrated on a fallenleaf in its bent and on state; the inset image was collected withexternal illumination. FIG. 29D provides data showing I-Vcharacteristics in the bent state as shown in FIG. 29C. FIG. 29Eprovides an optical image of a μ-ILED array integrated on paper in itsfolded and on state. FIG. 29F provides an optical image of a μ-ILEDarray on crumpled Al foil; the inset shows microscope image of fouradjacent pixels in their on states.

FIG. 30A provides data showing I-V characteristics of a 6×6 μ-ILED arrayintegrated on paper in its flat and folded state. FIG. 30B provides datashowing I-V characteristics of a 6×6 μ-ILED array integrated on Al foilin its flat and crumpled state. FIG. 30C provides data showing I-Vcharacteristics of a μ-ILED array integrated on paper as a function ofdeformation cycles (left) and voltage needed to generate a current of 20μA during a fatigue test (right). FIG. 30D provides data showing I-Vcharacteristics of a μ-ILED array integrated on Al foil as a function ofdeformation cycles (left) and voltage needed to generate a current of 20μA during a fatigue test (right).

FIG. 31A provides SEM images of a fabric before (left frame) and after(right frame) coating with a thin layer of PDMS. FIG. 31B provides SEMimages of Al foil before (left frame) and after (right frame) coatingwith a thin layer of PDMS. FIG. 31C provides SEM images of paper before(left frame) and after (right frame) coating with a thin layer of PDMS.FIG. 31D provides SEM images of a fallen leaf before (left frame) andafter (right frame) coating with a thin layer of PDMS.

FIGS. 32A, 32B and 32C provide optical images of μ-ILEDs integrated onflexible threads. FIG. 32D provides a schematic illustration describinga ‘rolling method’ for transfer printing. FIG. 32E provides an opticalimage of a 4×6 μ-ILED array on a glass tube using a rolling method forprinting. FIG. 32F provides an optical image showing a suturedemonstration using a μ-ILED array mounted on a thread at an incision inpaper.

FIG. 33 provides a schematic illustration of the encapsulation of animplantable array of μ-ILEDs.

FIG. 34A provides data showing the light intensity spectrum of a singleμ-ILED. FIGS. 34B and 34C provide data showing percent transmittance andtransmitted light intensity through a plasmonic crystal device as afunction of composition of fluid in contact with the plasmonic crystal.

FIGS. 35A, 35B and 35C provide data from a flexible plasmonic sensordevice, showing changes in detected intensity and refractive index asfunctions of composition of fluid in contact with the plasmonic crystal.

FIG. 36A provides data showing I-V characteristics of photodiodes atdifferent distances between an optical proximity sensor and anapproaching object. FIG. 36B provides data showing I-V characteristicsof a 2nd layer (an array of μ-IPDs). FIG. 36C provides data showingphotocurrent of an array of 6×6 p-IPDs that is stacked on the layer of a6×6 μ-ILEDs array as a function of operation current of μ-ILEDs in thestacked device. FIG. 36D provides data showing current-voltagecharacteristics of an array of 6×6 photodiodes as a function of distancebetween the device and the approaching object in the stacked device.FIG. 36E provides a re-plotting of FIG. 36D as a function of distancebetween approaching object and μ-IPDs.

FIGS. 37A and 37B provide data showing IV characteristics of a μ-ILEDarray at different immersion times.

FIG. 38A provides data showing the result of Luminance (L)—Current(I)—Voltage (V) measurement of an individual pixel with and withoutapplied ohmic contacts. FIG. 38B provides data showing applied voltageto generate a current of 20 μA, measured after different operationtimes.

FIG. 39A provides a schematic illustration of an analytical model forthe inflation and printing-down of PDMS film. FIGS. 39B and 39C provideresults of the FEM models.

FIG. 40 provides a schematic illustration of the cross section ofμ-ILEDs on a substrate.

FIG. 41A provides an overview image of two smart sutures.

FIG. 41B provides optical images of two smart sutures.

FIG. 41C provides data showing the resistance of a platinum temperaturesensor as a function of temperature.

FIG. 41D provides data showing temperature sensitivity of a silicondiode temperature sensor.

FIG. 41E provides I-V data for a temperature sensor for a number ofdifferent temperatures.

FIG. 41F provides an optical image of a smart suture.

FIG. 41G provides an overview image of a two sided smart suture.

FIG. 42A provides an overview of a model for determining the effect ofbending on a plasmonic crystal device and detector in a fluid monitor.FIG. 42B shows an expanded view of the model.

DETAILED DESCRIPTION

In general the terms and phrases used herein have their art-recognizedmeaning, which can be found by reference to standard texts, journalreferences and contexts known to those skilled in the art. The followingdefinitions are provided to clarify their specific use in the context ofthe invention.

“Transferable” or “printable” are used interchangeably and relates tomaterials, structures, device components and/or integrated functionaldevices that are capable of transfer, assembly, patterning, organizingand/or integrating onto or into substrates. In an embodiment,transferring or printing refers to the direct transfer of a structure orelement from one substrate to another substrate, such as from amultilayer structure to a device substrate or a device or componentsupported by a device substrate. Alternatively, transferable refers to astructure or element that is printed via an intermediate substrate, suchas a stamp that lifts-off the structure or element and then subsequentlytransfers the structure or element to a device substrate or a componentthat is on a device substrate. In an embodiment, the printing occurswithout exposure of the substrate to high temperatures (i.e. attemperatures less than or equal to about 400 degrees Celsius). In oneembodiment, printable or transferable materials, elements, devicecomponents and devices are capable of transfer, assembly, patterning,organizing and/or integrating onto or into substrates via solutionprinting or dry transfer contact printing. Similarly, “printing” is usedbroadly to refer to the transfer, assembly, patterning, organizingand/or integrating onto or into substrates, such as a substrate thatfunctions as a stamp or a substrate that is itself a target (e.g.,device) substrate. Such a direct transfer printing provides low-cost andrelatively simple repeated transfer of a functional top-layer of amultilayer structure to a device substrate. This achieves blankettransfer from, for example, a wafer to a target substrate without theneed for a separate stamp substrate.

“Substrate” refers to a material having a surface that is capable ofsupporting a component, including a device, component or aninterconnect. An interconnect that is “bonded” to the substrate refersto a portion of the interconnect in physical contact with the substrateand unable to substantially move relative to the substrate surface towhich it is bonded. Unbonded portions, in contrast, are capable ofsubstantial movement relative to the substrate. The unbonded portion ofan interconnect generally corresponds to that portion having a “bentconfiguration,” such as by strain-induced interconnect bending.

The term “surface” as used herein is intended to be consistent with itsplain meaning which refers to an outer boundary of an object. Inembodiments, surfaces may be given specific names, such as “receivingsurface”, “contact surface”, “external surface”. In some embodiments,named surfaces can refer to their target use and/or identify subregionsof a surface. In some embodiments, named surfaces can refer to theirorientation, for example relative to other nearby or adjacentcomponents.

“Functional layer” or “device layer” refers to a layer that imparts atleast partial functionality to that device or device component.Depending on the particular device or device component, a functionallayer can include a broad range of compositions. In contrast, afunctional layer for incorporation into electronics (MESFETs), LEDs, oroptical systems may have a different layering configuration and/orcompositions. Accordingly, the specific functional layer incorporatedinto a multilayer structure depends on the final device or devicecomponent in which the functional layer will be incorporated. Forexample, the functional layer may contain semiconductor components.Alternatively, the functional layer may comprise multiple layers, suchas multiple layers including a semiconductor separated by supportlayers. The functional layer may comprise a plurality of patternedelements, such as interconnects running between electrodes or islands.The functional layer may be heterogeneous or may have one or moreproperties that are inhomogeneous. “Inhomogeneous property” refers to aphysical parameter that can spatially vary, thereby effecting theposition of the neutral mechanical plane within a multilayer device.

“Structural layer” refers to a layer that imparts structuralfunctionality, for example by supporting and/or encapsulating devicecomponents.

“Buffer layer” refers to a layer of a device or device component whichis useful for protecting other layers of the device component. In oneembodiment, a buffer layer protects another device layer from etching.In an embodiment, a buffer layer does not impact or has a minimal impacton the function of the device. In one embodiment, an etch block layer isa buffer layer.

“Release” and “releasing” refer to at least partially separating twolayers, devices or device components from one another, for example bymechanical or physical separation, or by removal of at least a portionof one layer, device or device component. In some embodiments, removalof a sacrificial layer results in the release of a layer, device ordevice component. In some embodiments, layers, devices or devicecomponents are released by etching away a portion of the layer, deviceor device component. In certain embodiments, released components remainattached to the object with they are released from by one or moreanchors. In some embodiments, released components are subsequentlyattached to the object they are released from by one or more anchors.

The term “patterning” is used herein as in the art of microfabricationto broadly refer to a process by which portions of a layer, device ordevice component are selectively removed or deposited to create aspecified structure.

“Supported by a substrate” refers to a structure that is present atleast partially on a substrate surface or present at least partially onone or more intermediate structures positioned between the structure andthe substrate surface. The term “supported by a substrate” may alsorefer to structures partially or fully embedded in a substrate.

“Printable electronic device” or “printable electronic device component”refer to devices and structures that are configured for assembly and/orintegration onto substrate surfaces, for example by using dry transfercontact printing and/or solution printing methods. In embodiments, aprintable electronic device component is a printable semiconductorelement. In embodiments, printable semiconductor elements are unitarysingle crystalline, polycrystalline or microcrystalline inorganicsemiconductor structures. In various embodiments, printablesemiconductor elements are connected to a substrate, such as a motherwafer, via one or more bridge or anchor elements. In this context ofthis description, a unitary structure is a monolithic element havingfeatures that are mechanically connected. Semiconductor elements ofvarious embodiments may be undoped or doped, may have a selected spatialdistribution of dopants and may be doped with a plurality of differentdopant materials, including p- and n-type dopants. Certainmicrostructured printable semiconductor elements include those having atleast one cross sectional dimension greater than or equal to about 1 μmand nanostructured printable semiconductor elements having at least onecross sectional dimension less than or equal to about 1 μm.

Printable semiconductor elements useful for a variety of applicationscomprise elements derived from “top down” processing of high purity bulkmaterials, such as high purity crystalline semiconductor wafersgenerated using conventional high temperature processing techniques. Inan embodiment, a printable semiconductor element comprises a compositeheterogeneous structure having a semiconductor operationally connectedto or otherwise integrated with at least one additional device componentor structure, such as a conducting layer, dielectric layer, electrode,additional semiconductor structure or any combination of these. In somemethods and systems, the printable semiconductor element(s) comprises asemiconductor structure integrated with at least one additionalstructure selected from the group consisting of: another semiconductorstructure; a dielectric structure; conductive structure, and an opticalstructure (e.g., optical coatings, reflectors, windows, optical filter,collecting, diffusing or concentration optic etc.). In some embodimentsa printable semiconductor element comprises a semiconductor structureintegrated with at least one electronic device component selected fromthe group consisting of: an electrode, a dielectric layer, an opticalcoating, a metal contact pad and a semiconductor channel. In someembodiments, printable semiconductor elements comprise stretchablesemiconductor elements, bendable semiconductor elements and/orheterogeneous semiconductor elements (e.g., semiconductor structuresintegrated with one or more additional materials such as dielectrics,other semiconductors, conductors, ceramics etc.). Printablesemiconductor elements include printable semiconductor devices andcomponents thereof, including but not limited to printable LEDs, lasers,solar cells, p-n junctions, photovoltaics, photodiodes, diodes,transistors, integrated circuits, and sensors.

“Electronic device component” refers to a printable semiconductor orelectrical device. Exemplary electronic device component embodiments areconfigured for performing a function, for example emittingelectromagnetic radiation or converting electromagnetic radiation intoelectrical energy. In specific embodiments, multiple electronic devicecomponents are electrically interconnected and perform a more complextask or function than the individual device components perform alone.Useful electronic device components include, but are not limited to P-Njunctions, thin film transistors, single junction solar cells,multi-junction solar cells, photodiodes, light emitting diodes, lasers,CMOS devices, MOSFET devices, MESFET devices, photovoltaic cells,microelectricalmechanical devices and HEMT devices.

“Vertical type LED” refers to a light emitting diode device in which thefunctional components or layers of the device are arranged in a stackedconfiguration and the electrical contacts are made at the top and bottomof the stack. In some embodiments, a vertical type LED incorporates oneor more phosphor layers which absorb electromagnetic radiation of onewavelength or wavelength region and emit electromagnetic radiation of asecond wavelength or wavelength region.

“ON/OFF state” refers to a configuration of a device component capableof and/or configured for generation of electromagnetic radiation, suchas a light emitting diode or a laser. In one embodiment, an ON/OFF statedistinguishes between moments when a device component is generatingelectromagnetic radiation and when a device component is not generatingelectromagnetic radiation. In an embodiment, an ON/OFF statedistinguishes between moments when a device component is generatingelectromagnetic radiation having an intensity above a threshold valueand when a device component is generating electromagnetic radiationhaving an intensity below a threshold value.

“Solution printing” is intended to refer to processes whereby one ormore structures, such as transferable or printable elements, aredispersed into a carrier medium and delivered in a concerted manner toselected regions of a substrate surface. In an exemplary solutionprinting method, delivery of structures to selected regions of asubstrate surface is achieved by methods that are independent of themorphology and/or physical characteristics of the substrate surfaceundergoing patterning. Solution printing methods include, but are notlimited to, ink jet printing, thermal transfer printing, and capillaryaction printing.

“Contact printing” refers broadly to a dry transfer contact printingmethod such as with a stamp that facilitates transfer of features from astamp surface to a substrate surface. In an embodiment, the stamp is anelastomeric stamp. Alternatively, the transfer can be directly to atarget (e.g., device) substrate or host substrate. The followingreferences relate to self-assembly techniques which may be used inmethods described herein to transfer, assembly and interconnecttransferable semiconductor elements via contact printing and/or solutionprinting techniques and are incorporated by reference in theirentireties herein: (1) “Guided molecular self-assembly: a review ofrecent efforts”, Jiyun C Huie Smart Mater. Struct. (2003) 12, 264-271;(2) “Large-Scale Hierarchical Organization of Nanowire Arrays forIntegrated Nanosystems”, Whang, D.; Jin, S.; Wu, Y.; Lieber, C. M. NanoLett. (2003) 3(9), 1255-1259; (3) “Directed Assembly of One-DimensionalNanostructures into Functional Networks”, Yu Huang, Xiangfeng Duan,Qingqiao Wei, and Charles M. Lieber, Science (2001) 291, 630-633; and(4) “Electric-field assisted assembly and alignment of metallicnanowires”, Peter A. Smith et al., Appl. Phys. Lett. (2000) 77(9),1399-1401.

Useful contact printing methods for assembling, organizing and/orintegrating transferable elements include dry transfer contact printing,microcontact or nanocontact printing, microtransfer or nanotransferprinting and self-assembly assisted printing. Use of contact printing isbeneficial because it allows assembly and integration of a plurality oftransferable semiconductors in selected orientations and positionsrelative to each other. Contact printing also enables effectivetransfer, assembly and integration of diverse classes of materials andstructures, including semiconductors (e.g., inorganic semiconductors,single crystalline semiconductors, organic semiconductors, carbonnanomaterials etc.), dielectrics, and conductors. Contact printingmethods optionally provide high precision registered transfer andassembly of transferable semiconductor elements in preselected positionsand spatial orientations relative to one or more device componentsprepatterned on a device substrate. Contact printing is also compatiblewith a wide range of substrate types, including conventional rigid orsemi-rigid substrates such as glasses, ceramics and metals, andsubstrates having physical and mechanical properties attractive forspecific applications, such as flexible substrates, bendable substrates,shapeable substrates, conformable substrates and/or stretchablesubstrates. Contact printing assembly of transferable structures iscompatible, for example, with low temperature processing (e.g., lessthan or equal to 298K). This attribute allows optical systems to beimplemented using a range of substrate materials including those thatdecompose or degrade at high temperatures, such as polymer and plasticsubstrates. Contact printing transfer, assembly and integration ofdevice elements is also beneficial because it can be implemented via lowcost and high-throughput printing techniques and systems, such asroll-to-roll printing and flexographic printing methods and systems.

“Stretchable” refers to the ability of a material, structure, device ordevice component to be strained without undergoing fracture. In anexemplary embodiment, a stretchable material, structure, device ordevice component may undergo strain larger than about 0.5% withoutfracturing, preferably for some applications strain larger than about 1%without fracturing and more preferably for some applications strainlarger than about 3% without fracturing.

The terms “foldable,” “flexible” and “bendable” are used synonymously inthe present description and refer to the ability of a material,structure, device or device component to be deformed into a curved shapewithout undergoing a transformation that introduces significant strain,such as strain characterizing the failure point of a material,structure, device or device component. In an exemplary embodiment, aflexible material, structure, device or device component may be deformedinto a curved shape without introducing strain larger than or equal toabout 5%, preferably for some applications larger than or equal to about1%, and more preferably for some applications larger than or equal toabout 0.5%. A used herein, some, but not necessarily all, flexiblestructures are also stretchable. A variety of properties provideflexible structures (e.g., device components), including materialsproperties such as a low modulus, bending stiffness and flexuralrigidity; physical dimensions such as small average thickness (e.g.,less than 100 μm, optionally less than 10 μm and optionally less than 1μm) and device geometries such as thin film and mesh geometries.

“Semiconductor” refers to any material that is an insulator at very lowtemperatures, but which has an appreciable electrical conductivity attemperatures of about 300 Kelvin. In the present description, use of theterm semiconductor is intended to be consistent with use of this term inthe art of microelectronics and electrical devices. Usefulsemiconductors include element semiconductors, such as silicon,germanium and diamond, and compound semiconductors, such as group IVcompound semiconductors such as SiC and SiGe, group III-V semiconductorssuch as AlSb, AlAs, Aln, AIP, BN, GaSb, GaAs, GaN, GaP, InSb, InAs, InN,and InP, group III-V ternary semiconductors alloys such asAl_(x)Ga_(1-x)As, group II-VI semiconductors such as CsSe, CdS, CdTe,ZnO, ZnSe, ZnS, and ZnTe, group I-VII semiconductors CuCI, group IV-VIsemiconductors such as PbS, PbTe and SnS, layer semiconductors such asPbI₂, MoS₂ and GaSe, oxide semiconductors such as CuO and Cu₂O. The termsemiconductor includes intrinsic semiconductors and extrinsicsemiconductors that are doped with one or more selected materials,including semiconductor having p-type doping materials (also known asP-type or p-doped semiconductor) and/or n-type doping materials (alsoknown as N-type or n-doped semiconductor), to provide beneficialelectrical properties useful for a given application or device. The termsemiconductor includes composite materials comprising a mixture ofsemiconductors and/or dopants. Specific semiconductor materials usefulfor some embodiments include, but are not limited to, Si, Ge, Se,diamond, fullerenes, SiC, SiGe, SiO, SiO₂, SiN, AlSb, AlAs, AlIn, AIN,AIP, AIS, BN, BP, BAs, As₂S₃, GaSb, GaAs, GaN, GaP, GaSe, InSb, InAs,InN, InP, CsSe, CdS, CdSe, CdTe, Cd₃P₂, Cd₃As₂, Cd₃Sb₂, ZnO, ZnSe, ZnS,ZnTe, Zn₃P₂, Zn₃As₂, Zn₃Sb₂, ZnSiP₂, CuCl, PbS, PbSe, PbTe, FeO, FeS₂,NiO, EuO, EuS, PtSi, TIBr, CrBr₃, SnS, SnTe, PbI₂, MoS₂, GaSe, CuO,Cu₂O, HgS, HgSe, HgTe, HgI₂, MgS, MgSe, MgTe, CaS, CaSe, SrS, SrTe, BaS,BaSe, BaTe, SnO₂, TiO, TiO₂, Bi₂S₃, Bi₂O₃, Bi₂Te₃, BiI₃, UO₂, UO₃,AgGaS₂, PbMnTe, BaTiO₃, SrTiO₃, LiNbO₃, La₂CuO₄, Lao.₇Ca_(0.3)MnO₃,CdZnTe, CdMnTe, CuInSe₂, copper indium gallium selenide (CIGS), HgCdTe,HgZnTe, HgZnSe, PbSnTe, TI₂SnTe₅, TI₂GeTe₅, AlGaAs, AlGaN, AlGaP,AlInAs, AlInSb, AlInP, AlInAsP, AlGaAsN, GaAsP, GaAsN, GaMnAs, GaAsSbN,GalnAs, GaInP, AlGaAsSb, AlGaAsP, AlGaInP, GaInAsP, InGaAs, InGaP,InGaN, InAsSb, InGaSb, InMnAs, InGaAsP, InGaAsN, InAlAsN, GaInNAsSb,GaInAsSbP, and any combination of these. Porous silicon semiconductormaterials are useful in the field of sensors and light emittingmaterials, such as light emitting diodes (LEDs) and solid state lasers.Impurities of semiconductor materials are atoms, elements, ions and/ormolecules other than the semiconductor material(s) themselves or anydopants provided to the semiconductor material. Impurities areundesirable materials present in semiconductor materials which maynegatively impact the electrical properties of semiconductor materials,and include but are not limited to oxygen, carbon, and metals includingheavy metals. Heavy metal impurities include, but are not limited to,the group of elements between copper and lead on the periodic table,calcium, sodium, and all ions, compounds and/or complexes thereof.

“Semiconductor element”, “semiconductor structure” and “semiconductorcircuit element” are used synonymously in the present description andbroadly refer to any semiconductor material, composition, structure,device or device component, and expressly includes high quality, singlecrystalline and polycrystalline semiconductors, semiconductor materialsfabricated via high temperature processing, doped semiconductormaterials, inorganic semiconductors and composite semiconductormaterials and structures having one or more additional semiconductorcomponents and/or non-semiconductor components, such as dielectriclayers or materials and/or conducting layers or materials. In someembodiments, for example, semiconductor element refers to asemiconductor-containing device or component thereof, such as LEDs,lasers, solar cells, semiconductor junctions, p-n junctions,photovoltaics, photodiodes, diodes, transistors, integrated circuits,logic circuits, sensors, heaters, temperature sensors, thermistors andresistive heating elements. Semiconductor elements expressly includestructures having an average thickness selected over the range of 250 nmto 100 μm, one or more lateral dimensions selected over the range of 250nm to 100000 μm, and any combinations of these. Optionally semiconductorelements are provided in physical contact with other dielectric orinsulating materials and structures. Optionally, semiconductor elementsare provided in physical contact or electrical communication with othermetallic, doped or conducting materials and structures. Optionally,semiconductor structures are provided in physical contact or electricalcommunication with other semiconductor devices, including, but notlimited to LEDs, lasers, transistors, integrated circuits, logiccircuits, photodiodes, multiplexer circuitry and amplifier circuitry.Optionally, a plurality of semiconductor structures are provided inarray configurations, including arrays with a fixed element pitch or avariable element pitch. Semiconductor structures may optionally beprovided in a plurality of individually encapsulated stacked layers,including stacked layers of array structures. Semiconductor elementsutilized in the devices and methods described herein include high puritysemiconductor elements having oxygen impurities less than about 5 to 25parts per million atoms, carbon impurities less than about 1 to 5 partsper million atoms, and heavy metal impurities less than or equal toabout 1 part per million atoms (ppma), preferably less than or equal toabout 100 parts per billion atoms (ppba) for some applications, and morepreferably less than or equal to about 1 part per billion atoms (ppba)for some applications. Semiconductor elements having low levels of heavymetal impurities (e.g. less than about 1 parts per million atoms) arebeneficial for applications and devices requiring good electronicperformance, as the presence of heavy metals in semiconductor materialscan severely degrade their electrical properties.

In certain embodiments, the term “orientation” refers to a specificplane of a crystal structure, for example a semiconductor crystal. Incertain embodiments, the term “direction” refers to a specific axis, orequivalent axes, of a crystal structure. In embodiments, use of theterms orientation and direction with a specific numeric indicator isintended to be consistent with use in the fields of crystallography andmicrofabrication.

“Quantum well” refers to an active layer of a light emitting diodedevice. In one embodiment, a quantum well is a layer of an LED devicehaving a relatively narrow bandgap, surrounded on two sides by layershaving a relatively wider bandgap. A “quantum well barrier layer” in thecontext of a subcomponent of a light emitting diode refers to a layer ofa light emitting diode device which is positioned adjacent to a quantumwell layer and has a larger bandgap than the quantum well material. Inone embodiment, a quantum well layer is sandwiched between two quantumwell barrier layers. In another embodiment, multiple quantum well layersare sandwiched between multiple quantum well barrier layers.

“Good electronic performance” and “high performance” are usedsynonymously in the present description and refer to devices and devicecomponents have electronic characteristics, such as field effectmobilities, threshold voltages and on—off ratios, providing a desiredfunctionality, such as electronic signal switching and/or amplification.Exemplary printable elements exhibiting good electronic performance mayhave intrinsic field effect mobilities greater than or equal 100 cm² V⁻¹5⁻¹, and for some applications, greater than or equal to about 300 cm²V⁻¹ s⁻¹. Exemplary transistors exhibiting good electronic performancemay have device field effect mobilities great than or equal to about 100cm² V⁻¹ 5⁻¹, for some applications, greater than or equal to about 300cm² V⁻¹ 5⁻¹, and for other applications, greater than or equal to about800 cm² V⁻¹ s⁻¹. Exemplary transistors of exhibiting good electronicperformance may have threshold voltages less than about 5 volts and/oron—off ratios greater than about 1×10⁴.

“Plastic” refers to any synthetic or naturally occurring material orcombination of materials that can be molded or shaped, generally whenheated, and hardened into a desired shape. Useful plastics include, butare not limited to, polymers, resins and cellulose derivatives. In thepresent description, the term plastic is intended to include compositeplastic materials comprising one or more plastics with one or moreadditives, such as structural enhancers, fillers, fibers, plasticizers,stabilizers or additives which may provide desired chemical or physicalproperties.

“Prepolymer” refers to a material which is a polymer precursor and/or amaterial which, when cured, is a polymer. A “liquid prepolymer” refersto a prepolymer which exhibits one or more properties of a liquid, forexample flow properties. Specific prepolymers include, but are notlimited to, photocurable polymers, thermally curable polymers andphotocurable polyurethanes.

“Curing” refers to a process by which a material is transformed suchthat the transformed material exhibits one or more properties differentfrom the original, non-transformed material. In some embodiments, acuring process allows a material to become solid or rigid. In anembodiment, curing transforms a prepolymer material into a polymermaterial. Useful curing processes include, but are not limited to,exposure to electromagnetic radiation (photocuring processes), forexample exposure to electromagnetic radiation of a specific wavelengthor wavelength range (e.g., ultraviolet or infrared electromagneticradiation); thermal curing processes, for example heating to a specifictemperature or within a specific temperature range (e.g., 150° C. orbetween 125 and 175° C.); temporal curing processes, for example waitingfor a specified time or time duration (e.g., 5 minutes or between 10 and20 hours); drying processes, for example removal of all or a percentageof water or other solvent molecules; and any combination of these. Forexample, one embodiment for curing a silver epoxy comprises heating thesilver epoxy to 150° C. for a duration of 5 minutes.

“Polymer” refers to a molecule comprising a plurality of repeatingchemical groups, typically referred to as monomers. Polymers are oftencharacterized by high molecular masses. Polymers are typically composedof repeating structural units connected by covalent chemical bonds orthe polymerization product of one or more monomers. The term polymerincludes homopolymers, or polymers consisting essentially of a singlerepeating monomer subunit. The term polymer also includes copolymers, orpolymers consisting essentially of two or more monomer subunits, such asrandom, block, alternating, segmented, graft, tapered and othercopolymers. Useful polymers include organic polymers and inorganicpolymers, both of which may be in amorphous, semi-amorphous, crystallineor partially crystalline states. Polymers may comprise monomers havingthe same chemical composition or may comprise a plurality of monomershaving different chemical compositions, such as a copolymer. Crosslinked polymers having linked monomer chains are also useful for someembodiments. Useful polymers include, but are not limited to, plastics,elastomers, thermoplastic elastomers, elastoplastics, thermoplastics andacrylates. Exemplary polymers include, but are not limited to, acetalpolymers, biodegradable polymers, cellulosic polymers, fluoropolymers,nylons, polyacrylonitrile polymers, polyimide-imide polymers,polyimides, polyarylates, polybenzimidazole, polybutylene,polycarbonate, polyesters, polyetherimide, polyethylene, polyethylenecopolymers and modified polyethylenes, polyketones, poly(methylmethacrylate, polymethylpentene, polyphenylene oxides and polyphenylenesulfides, polyphthalamide, polypropylene, polyurethanes, styrenicresins, sulfone based resins, vinyl-based resins, rubber (includingnatural rubber, styrene-butadiene, polybutadiene, neoprene,ethylene-propylene, butyl, nitrile, silicones), acrylic, polystyrene,polyvinyl chloride, polyolefin or any combinations of these.

“Elastomer” refers to a polymeric material which can be stretched ordeformed and return to its original shape without substantial permanentdeformation. Elastomers commonly undergo substantially elasticdeformations. Useful elastomers may comprise polymers, copolymers,composite materials or mixtures of polymers and copolymers. Anelastomeric layer refers to a layer comprising at least one elastomer.Elastomeric layers may also include dopants and other non-elastomericmaterials. Useful elastomer embodiments include, but are not limited to,thermoplastic elastomers, styrenic materials, olefenic materials,polyolefin, polyurethane thermoplastic elastomers, polyamides, syntheticrubbers, PDMS, polybutadiene, polyisobutylene,poly(styrene-butadiene-styrene), polyurethanes, polychloroprene andsilicones. In some embodiments, an elastomeric stamp comprises anelastomer. Exemplary elastomers include, but are not limited to siliconcontaining polymers such as polysiloxanes including poly(dimethylsiloxane) (i.e. PDMS and h-PDMS), poly(methyl siloxane), partiallyalkylated poly(methyl siloxane), poly(alkyl methyl siloxane) andpoly(phenyl methyl siloxane), silicon modified elastomers, thermoplasticelastomers, styrenic materials, olefenic materials, polyolefin,polyurethane thermoplastic elastomers, polyam ides, synthetic rubbers,polyisobutylene, poly(styrene-butadiene-styrene), polyurethanes,polychloroprene and silicones. In an embodiment, a flexible polymer is aflexible elastomer.

“Transfer device” or “transfer substrate” refers to a substrate, deviceor device component capable of and/or configured for receiving and/orrelocating an element or array of elements, such as printable elements.Useful transfer devices include conformal transfer devices, such asdevices having one or more contact surfaces capable of establishingconformal contact with elements undergoing transfer. An elastomericstamp and/or transfer device is useful with a variety of the methods anddevices described herein. Useful elastomeric transfer devices include,but are not limited to, elastomeric stamps, composite elastomericstamps, an elastomeric layer, a plurality of elastomeric layers and anelastomeric layer coupled to a substrate such as a glass, ceramic, metalor polymer substrate.

“Elastomeric stamp” or “elastomeric transfer device” are usedinterchangeably and refer to an elastomeric material having a surfacethat can receive as well as transfer a feature. Exemplary elastomerictransfer devices include stamps, molds and masks. The transfer deviceaffects and/or facilitates feature transfer from a donor material to areceiver material. Stamps and transfer device may be used for assemblingcomponents via transfer printing, such as dry contact transfer printing.

“Target substrate” is used broadly to refer to the desired finalsubstrate that will support the transferred structure. In an embodiment,the target substrate is a device substrate. In an embodiment, the targetsubstrate is a device component or element that is itself supported by asubstrate.

“Large area” refers to an area, such as the area of a receiving surfaceof a substrate used for device fabrication, greater than or equal toabout 36 square inches.

“Pre-metalized” refers to a structure which includes metallic layers,components or features.

“Pre-patterned” refers to a structure which includes one or moredevices, components or relief features.

“Optical communication” refers to a configuration of two or moreelements wherein one or more beams of electromagnetic radiation arecapable of propagating from one element to the other element. Elementsin optical communication may be in direct optical communication orindirect optical communication. “Direct optical communication” refers toa configuration of two or more elements wherein one or more beams ofelectromagnetic radiation propagate directly from a first device elementto another without use of optical components for steering and/orcombining the beams. “Indirect optical communication” refers to aconfiguration of two or more elements wherein one or more beams ofelectromagnetic radiation propagate between two elements via one or moredevice components including, but not limited to, wave guides, fiberoptic elements, reflectors, filters, prisms, lenses, gratings and anycombination of these device components.

“Electrical contact” and “electrical communication” refers to thearrangement of one or more objects such that an electric currentefficiently flows from one object to another. For example, in someembodiments, two objects having an electrical resistance between themless than 100Ω are considered in electrical communication with oneanother. An electrical contact can also refer to a component of a deviceor object used for establishing electrical communication with externaldevices or circuits, for example an electrical interconnection.“Electrical contact” also refers to the ability of two or more materialsand/or structures that are capable of transferring charge between them,such as in the form of the transfer of electrons or ions. “Electricalcommunication” also refers to a configuration of two or more componentssuch that an electronic signal or charge carrier can be directly orindirectly transferred from one component to another. As used herein,electrical communication includes one way and two way electricalcommunication. In some embodiments, components in electricalcommunication are in direct electrical communication wherein anelectronic signal or charge carrier is directly transferred from onecomponent to another. In some embodiments, components in electricalcommunication are in indirect electrical communication wherein anelectronic signal or charge carrier is indirectly transferred from onecomponent to another via one or more intermediate structures, such ascircuit elements, separating the components.

“Electrical resistivity” refers to a property of a materialcharacteristic of the resistance to flow of electrons through thematerial. In certain embodiments, the resistivity of a material (ρ) isrelated to the resistance (R) of a length of material (L) having aspecific cross sectional area (A), e.g., ρ=R×A/L.

“Electrical interconnection” and “electrical interconnect” refers to acomponent of an electrical device used for providing electricalcommunication between two or more device components. In someembodiments, an electrical interconnect is used to provide electricalcommunication between two device components spatially separated from oneanother, for example spatially separated by a distance greater than 50nm, for some applications greater than 100 nm, for other applicationsgreater than 1 μm, and for yet other applications greater than 50 μm.“Electrode contact” refers to a component of an electronic device ordevice component to which an electrical interconnect attaches orprovides electrical communication to or from.

“Embed” refers to a process by which one object or device is buried,conformally surrounded or otherwise placed or positioned within or belowthe surface another object, layer or material.

“Encapsulate” refers to the orientation of one structure such that it isentirely surrounded by one or more other structures. “Partiallyencapsulated” refers to the orientation of one structure such that it ispartially surrounded by one or more other structures. “Completelyencapsulated” refers to the orientation of one structure such that it iscompletely surrounded by one or more other structures. Some embodimentscontemplate devices having partially or completely encapsulatedelectronic devices, device components and/or inorganic semiconductorcomponents and/or electrodes.

“Replicate” refers to a process by which one or more relief features aretransferred and/or recreated during casting, molding, embedding, orembossing processes. Replicated features generally resemble the featuresthey originate from except that the replicated features represent thenegative of the original features; that is where the original featuresare raised features, the replicated features are recessed features andwhere the original features are recessed features, the replicatedfeatures are raised features. “Replica molding” and “nano imprintlithography” refer to specific replicating methods known in the art ofmicrofabrication.

“Relief feature” refers to portions of an object or layer exhibitingdifferences in elevation and slope between the higher and lower parts ofthe surface of a given area or portion of the object or layer. “Raisedfeatures” refer to relief features which extend above the surface oraverage surface level of an object or layer or relief features whichhave elevations higher than other portions of the surface of an objector layer. “Recessed feature” refer to relief features which extend belowthe surface or average surface level of an object or layer or relieffeatures which have elevations lower than other portions of the surfaceof an object or layer.

“Unitary structure” refers to a structure having one or more componentswithin a single continuous or monolithic body, and includes structureshaving a uniform or non-uniform composition.

“Conformal contact” refers to contact established between surfaces,coated surfaces, and/or surfaces having materials deposited thereonwhich may be useful for transferring, assembling, organizing andintegrating structures (such as printable elements) on a substratesurface. In one aspect, conformal contact involves a macroscopicadaptation of one or more contact surfaces of a conformal transferdevice to the overall shape of a substrate surface or the surface of anobject such as a printable element. In another aspect, conformal contactinvolves a microscopic adaptation of one or more contact surfaces of aconformal transfer device to a substrate surface leading to an intimatecontact without voids. The term conformal contact is intended to beconsistent with use of this term in the art of soft lithography.Conformal contact may be established between one or more bare contactsurfaces of a conformal transfer device and a substrate surface.Alternatively, conformal contact may be established between one or morecoated contact surfaces, for example contact surfaces having a transfermaterial, printable element, device component, and/or device depositedthereon, of a conformal transfer device and a substrate surface.Alternatively, conformal contact may be established between one or morebare or coated contact surfaces of a conformal transfer device and asubstrate surface coated with a material such as a transfer material,solid photoresist layer, prepolymer layer, liquid, thin film or fluid.

“Conformable” refers to a device, material or substrate which has abending stiffness sufficiently low to allow the device, material orsubstrate to adopt any desired contour profile, for example a contourprofile allowing for conformal contact with a surface having a patternof relief features. In certain embodiments, a desired contour profile isthat of a tissue in a biological environment,

“Bind” and “bond” refers to the physical attachment of one object toanother. Bind and bound can also refer the retention of one object onanother. In one embodiment an object can bind to another by establishinga force between the objects. In some embodiments, objects are bound toone another through use of an adhesion layer. In one embodiment, anadhesion layer refers to a layer used for establishing a bonding forcebetween two objects.

“Placement accuracy” refers to the ability of a transfer method ordevice to transfer a printable element, to a selected position, eitherrelative to the position of other device components, such as electrodes,or relative to a selected region of a receiving surface. “Good placementaccuracy” refers to methods and devices capable of transferring aprintable element to a selected position relative to another device ordevice component or relative to a selected region of a receiving surfacewith spatial deviations from the absolutely correct position less thanor equal to 50 μm, more preferably less than or equal to 20 μm for someapplications and even more preferably less than or equal to 5 μm forsome applications. Methods and devices described herein include thosecomprising at least one printable element transferred with goodplacement accuracy.

“Fidelity” refers to a measure of how well a selected pattern ofelements, such as a pattern of printable elements, is transferred to areceiving surface of a substrate. Good fidelity refers to transfer of aselected pattern of elements wherein the relative positions andorientations of individual elements are preserved during transfer, forexample wherein spatial deviations of individual elements from theirpositions in the selected pattern are less than or equal to 500 nm, morepreferably less than or equal to 100 nm.

“Undercut” refers to a structural configuration wherein the bottomsurfaces of an element, such as a printable element, bridge elementand/or anchor element, are at least partially detached from or not fixedto another structure, such as a mother wafer or bulk material. Entirelyundercut refers to a refers to a structural configuration wherein thebottom surfaces of an element, such as printable element, bridge elementand/or anchor element, is completely detached from another structure,such as a mother wafer or bulk material. Undercut structures may bepartially or entirely free standing structures. Undercut structures maybe partially or fully supported by another structure, such as a motherwafer or bulk material, that they are detached from. Undercut structuresmay be attached, affixed and/or connected to another structure, such asa wafer or other bulk material, at surfaces other than the bottomsurfaces.

“Anchor” refers to a structure useful for connecting or tethering onedevice or device component to another. “Anchoring” refers to a processresulting in the connection or tethering of one device or devicecomponent to another.

“Homogeneous anchoring” refers to an anchor that is an integral part ofthe functional layer. In general, methods of making transferableelements by homogenous anchoring systems is optionally by providing awafer, depositing a sacrificial layer on at least a portion of a wafersurface, defining semiconductor elements by any means known in the art,and defining anchor regions. The anchor regions correspond to specificregions of the semiconductor element. The anchor regions can correspondto a geometrical configuration of a semiconductor layer, e.g., anchorsdefined by relatively large surface areas and are connected totransferable elements by bridge or tether elements. Such geometryprovides a means for facilitating lift-off of specific non-anchoredregions for either single-layer or multi-layer embodiments.Alternatively, anchors correspond to semiconductor regions that areattached or connected to the underlying wafer. Removing the sacrificiallayer provides a means for removing or transferring semiconductorelements while the portion of semiconductor physically connected to theunderlying wafer remains.

“Heterogeneous anchoring” refers to an anchor that is not an integralpart of the functional layer, such as anchors that are made of adifferent material than the semiconductor layer or is made of the samematerial, but that is defined after the transferable semiconductorelements are placed in the system. One advantage of heterogeneousanchoring compared to homogeneous anchoring relates to better transferdefining strategies and further improvement to the effective useablewafer footprint. In the heterogeneous strategy embodiment, a wafer isprovided, the wafer is coated with a sacrificial layer, semiconductorelements are defined, and heterogeneous anchor elements are depositedthat anchor semiconductor regions. In an aspect, the anchor is a resistmaterial, such as a photoresist or SiN (silicon nitride), or othermaterial that has a degree of rigidity capable of anchoring andresisting a lift-off force that is not similarly resisted bynon-anchored regions. The anchor may span from the top-mostsemiconductor layer through underlying layers to the underlying wafersubstrate. Removal of sacrificial layer provides a means for removingunanchored regions while the anchored regions remain connected to thewafer, such as by contact transfer, for example. In another embodiment,for a multi-layer system, the anchor provides anchoring of a top layerto an underlying semiconductor layer. Alternatively, the anchoringsystem is for single-layer semiconductor layer systems.

“Carrier film” refers to a material that facilitates separation oflayers. The carrier film may be a layer of material, such as a metal ormetal-containing material positioned adjacent to a layer that is desiredto be removed. The carrier film may be a composite of materials,including incorporated or attached to a polymeric material orphotoresist material, wherein a lift-off force applied to the materialprovides release of the composite of materials from the underlying layer(such as a functional layer, for example).

A “NMS adjusting layer” refers to a layer whose primary function isadjusting the position of the NMS in the device. For example, the NMSadjusting layer may be an encapsulating layer or an add layer such as anelastomeric material.

In the context of this description, a “bent configuration” refers to astructure having a curved conformation resulting from the application ofa force. Bent structures may have one or more folded regions, convexregions, concave regions, and any combinations thereof. Useful bentstructures useful, for example, may be provided in a coiledconformation, a wrinkled conformation, a buckled conformation and/or awavy (i.e., wave-shaped) configuration.

Bent structures, such as stretchable bent interconnects, may be bondedto a flexible substrate, such as a polymer and/or elastic substrate, ina conformation wherein the bent structure is under strain. In someembodiments, the bent structure, such as a bent ribbon structure, isunder a strain equal to or less than about 30%, a strain equal to orless than about 10%, a strain equal to or less than about 5% and astrain equal to or less than about 1% in embodiments preferred for someapplications. In some embodiments, the bent structure, such as a bentribbon structure, is under a strain selected from the range of about0.5% to about 30%, a strain selected from the range of about 0.5% toabout 10%, a strain selected from the range of about 0.5% to about 5%.Alternatively, the stretchable bent interconnects may be bonded to asubstrate that is a substrate of a device component, including asubstrate that is itself not flexible. The substrate itself may beplanar, substantially planar, curved, have sharp edges, or anycombination thereof. Stretchable bent interconnects are available fortransferring to any one or more of these complex substrate surfaceshapes.

“Thermal contact” or “thermal communication” refers to the ability oftwo materials that are capable of substantial heat transfer from thehigher temperature material to the lower temperature material, such asby conduction. Bent structures resting on a substrate are of particularuse in providing regions that are in thermal contact (e.g., bondregions) with the substrate and other regions that are not in thermalcontact (e.g., regions that are insulated and/or physically separatedfrom the substrate).

“Fluid communication” refers to the configuration of two or morecomponents such that a fluid (e.g., a gas or a liquid) is capable oftransport, flowing and/or diffusing from one component to anothercomponent. Elements may be in fluid communication via one or moreadditional elements such as tubes, containment structures, channels,valves, pumps or any combinations of these. In some embodiments,components in fluid communication are in direct fluid communicationwherein fluid is capable of transport directly from one component toanother. In some embodiments, components in fluid communication are inindirect fluid communication wherein fluid is capable of transportindirectly from one component to another via one or more intermediatestructures separating the components.

“Ultrathin” refers to devices of thin geometries that exhibit extremelevels of bendability. In an embodiment, ultrathin refers to circuitshaving a thickness less than 1 μm, less than 600 nm or less than 500 nm.In an embodiment, a multilayer device that is ultrathin has a thicknessless than 200 μm, less than 50 μm, or less than 10 μm.

“Thin layer” refers to a material that at least partially covers anunderlying substrate, wherein the thickness is less than or equal to 300μm, less than or equal to 200 μm, or less than or equal to 50 μm.Alternatively, the layer is described in terms of a functionalparameter, such as a thickness that is sufficient to isolate orsubstantially reduce the strain on the electronic device, and moreparticularly a functional layer in the electronic device that issensitive to strain.

“Isolate” refers to the presence of an elastomer layer thatsubstantially reduces the strain or stress exerted on a functional layerwhen the device undergoes a stretching of folding deformation. In anembodiment, strain is said to be “substantially” reduced if the strainis at least a factor of 20, at least a factor of 50 or at least a factorof 100 times reduced compared to the strain in the same system withoutthe elastomer layer.

“Dielectric” and “dielectric material” are used synonymously in thepresent description and refer to a substance that is highly resistant toflow of electric current. Useful dielectric materials include, but arenot limited to, SiO₂, Ta₂O₅, TiO₂, ZrO₂, Y₂₀₃, Si₃N₄, STO, BST, PLZT,PMN, and PZT. In some embodiments, dielectric materials includenon-conducting or insulating materials. In an embodiment, an inorganicdielectric comprises a dielectric material substantially free of carbon

“Device field effect mobility” refers to the field effect mobility of anelectronic device, such as a transistor, as computed using outputcurrent data corresponding to the electronic device. In an embodiment,an inorganic dielectric comprises a dielectric material substantiallyfree of carbon. Specific examples of inorganic dielectric materialsinclude, but are not limited to, silicon nitride and silicon dioxide.

“Fill factor” refers to the percentage of the area between two elements,such as between two electrodes, that is occupied by a material, elementand/or device component. In one embodiment, two electrodes are providedin electrical contact with one or more printable semiconductor elementsthat provide a fill factor between first and second electrodes greaterthan or equal to 20%, preferably greater than or equal to 50% for someapplications and more preferably greater than or equal to 80% for someapplications. In some embodiments, high fill factors are provided bystacking functional layers above/below one another.

“Multilayer stacked geometry” refers to a device comprising a pluralityof functional layers in a stacked configuration. In some embodiments,stacked multilayers are provided in an offset configuration such thatone or more device components in a first functional layer are notprovided directly adjacent to one or more device components in a secondfunctional layer, such as a first functional layer positioned adjacentto, above or below a second functional layer.

“Collecting” and “concentrating”, as applied to optics and opticalcomponents, refers to the characteristic of optical components anddevice components that collect light from a first area, in some cases alarge area, and optionally direct that light to another area, in somecases a relatively smaller area. In the context of some embodiments,collecting and concentrating optical components and/or opticalcomponents are useful for light detection or power harvesting by printedsolar cells or photodiodes.

“Conductive material” refers to a substance or compound possessing anelectrical resistivity which is typical of or equivalent to that of ametal, for example copper, silver or aluminum. In embodiments, theelectrical resistivity of a conductive material is selected over therange of 1×10⁻¹° to 1×10⁻² Ω·cm. In the present description, use of theterm conductive material is intended to be consistent with use of thisterm in the art of electronic devices and electric circuits. Inembodiments, conductive materials are useful as electricalinterconnections and/or for providing electrical communication betweentwo devices. A “conductive paste” refers to a conductive materialcomprising a mixture which is generally soft and malleable. In someembodiments, cured conductive pastes lose their soft and malleablenature and generally exhibit properties of a solid or a monolithic body.Exemplary conductive pastes comprise metal micro- and/or nano-particles.Silver epoxy refers to a conductive paste comprising micro- and/or nanoparticles including metallic silver (Ag) and which, when cured, exhibitsa low electrical resistivity, for example an electrical resistivitylower than 1×10⁻⁵ Ω·cm or selected over the range of 1×10⁻¹⁰ to 1×10⁻⁵Ω·cm.

“Fill” and “filling” refer to a process of depositing a material into arecessed feature. In one embodiment, a recessed region is filled byscraping material across and into the recessed feature. A filling toolgenerally refers to a device for moving material into a recessedfeature. In an embodiment, a filling tool refers to a device forscraping material across and/or into a recessed region. In a specificembodiment, a filling tool comprises a layer or solid body of PDMS. Forcertain embodiments, a filling process is conceptually similar to ascreen printing process where a material is scraped across a recessedfeature by a tool or device having dimensions larger than the recessedfeature, thereby at least partially filling the recessed feature withthe material.

“Align” refers to a process by which two objects are arranged withrespect to one another. “Aligned off center” refers to a process bywhich the centers of two objects or two areas are arranged such that thetwo centers are not coincident with respect to one or more spatialdimensions. For certain embodiments, the term aligned off center refersto alignment of the center of two objects such that the centers of theobjects are spatially separated by a distance greater than 50 nm, forsome applications greater than 100 nm, for other applications greaterthan 1 μm, and for yet other applications greater than 50 μm.

“Neutral mechanical surface,” “NMS,” “neutral mechanical plane,” and“NMP” interchangeably refer to a position within a device or componentunder strain that experiences an absence of strain. In some embodimentsa NMS or NMP is a plane positioned between two regions or layers of adevice or component under strain, such as a plane between regions undercompressive strain and regions under expansive strain. The NMP is lesssusceptible to bending stress than other planes of the device that lieat more extreme positions along a vertical axis of the device and/orwithin more bendable layers of the device. Thus, the position of the NMPis determined by both the thickness of the device and the materialsforming the layer(s) of the device.

“Coincident” refers to refers to the relative position of two or moreobjects, planes or surfaces, for example a surface such as a NMS or NMPthat is positioned within or is adjacent to a layer, such as afunctional layer, substrate layer, or other layer. In an embodiment, aNMS or NMP is positioned to correspond to the most strain-sensitivelayer or material within the layer.

“Proximate” refers to the relative position of two or more objects,planes or surfaces. For example, a NMS or NMP that is proximate to orclosely follows the position of a layer, such as a functional layer,substrate layer, or other layer while still providing desiredfoldability or bendability without an adverse impact on thestrain-sensitive material physical properties. “Strain-sensitive” refersto a material that fractures or is otherwise impaired in response to arelatively low level of strain. In general, a layer having a high strainsensitivity, and consequently being prone to being the first layer tofracture, is located in the functional layer, such as a functional layercontaining a relatively brittle semiconductor or other strain-sensitivedevice element. A NMS or NMP that is proximate to a layer need not beconstrained within that layer, but may be positioned proximate orsufficiently near to provide a functional benefit of reducing the strainon the strain-sensitive device element when the device is folded.

“Electronic device” is used broadly herein to refer to devices such asintegrated circuits, imagers or other optoelectronic devices. Electronicdevice may also refer to a component of an electronic device such aspassive or active components such as a semiconductor, interconnect,contact pad, transistors, diodes, LEDs, circuits, etc. Devices disclosedherein may relate to the following fields: collecting optics, diffusingoptics, displays, pick and place assembly, vertical cavitysurface-emitting lasers (VCSELS) and arrays thereof, LEDs and arraysthereof, transparent electronics, photovoltaic arrays, solar cells andarrays thereof, flexible electronics, micromanipulation, plasticelectronics, displays, pick and place assembly, transfer printing, LEDs,transparent electronics, stretchable electronics, and flexibleelectronics.

A “component” is used broadly to refer to a material or individualcomponent used in a device. An “interconnect” is one example of acomponent and refers to an electrically conducting material capable ofestablishing an electrical connection with a component or betweencomponents. In particular, an interconnect may establish electricalcontact between components that are separate and/or can move withrespect to each other. Depending on the desired device specifications,operation, and application, an interconnect is made from a suitablematerial. For applications where a high conductivity is required,typical interconnect metals may be used, including but not limited tocopper, silver, gold, aluminum and the like, and alloys. Suitableconductive materials further include semiconductors, such as silicon andGaAs and other conducting materials such as indium tin oxide.

Other components include, but are not limited to, thin film transistors(TFTs), transistors, electrodes, integrated circuits, circuit elements,control elements, microprocessors, transducers, islands, bridges andcombinations thereof. Components may be connected to one or more contactpads as known in the art, such as by metal evaporation, wire bonding,and application of solids or conductive pastes, for example.

An interconnect that is “stretchable” or “flexible” is used herein tobroadly refer to an interconnect capable of undergoing a variety offorces and strains such as stretching, bending and/or compression in oneor more directions without adversely impacting electrical connection to,or electrical conduction from, a device component. Accordingly, astretchable interconnect may be formed of a relatively brittle material,such as GaAs, yet remain capable of continued function even when exposedto a significant deformatory force (e.g., stretching, bending,compression) due to the interconnect's geometrical configuration. In anexemplary embodiment, a stretchable interconnect may undergo strainlarger than about 1%, 10% or about 30% or up to about 100% withoutfracturing. In an example, the strain is generated by stretching anunderlying elastomeric substrate to which at least a portion of theinterconnect is bonded. For certain embodiments, flexible or stretchableinterconnects include interconnects having wavy, meandering orserpentine shapes.

A “device component” is used to broadly refer to an individual componentwithin an electrical, optical, mechanical or thermal device. Componentsinclude, but are not limited to, a photodiode, LED, TFT, electrode,semiconductor, other light-collecting/detecting components, transistor,integrated circuit, contact pad capable of receiving a device component,thin film devices, circuit elements, control elements, microprocessors,transducers and combinations thereof. A device component can beconnected to one or more contact pads as known in the art, such as metalevaporation, wire bonding, application of solids or conductive pastes,for example. Electrical device generally refers to a deviceincorporating a plurality of device components, and includes large areaelectronics, printed wire boards, integrated circuits, device componentsarrays, biological and/or chemical sensors, physical sensors (e.g.,temperature, light, radiation, etc.), solar cell or photovoltaic arrays,display arrays, optical collectors, systems and displays.

“Sensing element” and “sensor” are used synonymously and refers to adevice component useful as a sensor and/or useful for detecting thepresence, absence, amount, magnitude or intensity of a physicalproperty, object, radiation and/or chemical. Sensors in some embodimentsfunction to transduce a biological signal into an electrical signal,optical signal, wireless signal, acoustic signal, etc. Useful sensingelements include, but are not limited to electrode elements, chemical orbiological sensor elements, pH sensors, optical sensors, photodiodes,temperature sensors, capacitive sensors strain sensors, accelerationsensors, movement sensors, displacement sensors, pressure sensors,acoustic sensors or combinations of these.

“Sensing” refers to detecting the presence, absence, amount, magnitudeor intensity of a physical and/or chemical property. Useful electronicdevice components for sensing include, but are not limited to electrodeelements, chemical or biological sensor elements, pH sensors,temperature sensors and capacitive sensors.

“Actuating element” and “actuator” are used synonymously and refers to adevice component useful for interacting with, stimulating, controlling,or otherwise affecting an external structure, material or fluid, forexample a biological tissue. Useful actuating elements include, but arenot limited to, electrode elements, electromagnetic radiation emittingelements, light emitting diodes, lasers and heating elements. Actuatingelements include electrodes for providing a voltage or current to atissue. Actuating elements include sources of electromagnetic radiationfor providing electromagnetic radiation to a tissue. Actuating elementsinclude ablation sources for ablating tissue. Actuating elements includethermal sources for heating tissue. Actuating elements includedisplacement sources for displacing or otherwise moving a tissue. Insome embodiments, actuating elements are used for interacting with,modifying a property of or otherwise affecting a device component, forexample a barrier layer.

“Actuating” refers to stimulating, controlling, or otherwise affectingan external structure, material or fluid, for example a biologicaltissue. Useful electronic device components for actuating include, butare not limited to, electrode elements, electromagnetic radiationemitting elements, light emitting diodes, lasers, and heating elements.

“Visualizing” refers to a method of observing or otherwise detectingelectromagnetic radiation, for example with an eye or a photodetector.

“Island” or “device island” refers to a relatively rigid device elementor component of an electronic device comprising multiple semiconductorelements or active semiconductor structures. “Bridge” or “bridgestructure” refers to stretchable or flexible structures interconnectingtwo or more device islands or one device island to another devicecomponent. Specific bridge structures include flexible semiconductorinterconnects.

“Barrier layer” refers to a device component spatially separating two ormore other device components or spatially separating a device componentfrom a structure, material or fluid external to the device. In oneembodiment, a barrier layer encapsulates one or more device components.In embodiments, a barrier layer is an encapsulation layer. Inembodiments, a barrier layer separates one or more device componentsfrom an aqueous solution, a biological tissue or both. In someembodiments, a barrier layer is a passive device component. In someembodiments, a barrier layer is a functional, but non-active, devicecomponent. In a specific embodiment, a barrier layer is a moisturebarrier. As used herein, the terms “moisture barrier” and “barrier layerpreventing water from contacting” refers to a barrier layer whichprovides protection to other device components from water or othersolvents. In one embodiment, a moisture barrier provides protection toan external structure, material or fluid, for example, by preventingleakage current from escaping an encapsulated device component andreaching the external structure, material or fluid. In a specificembodiment, a barrier layer is a thermal barrier. As used herein, theterm “thermal barrier” refers to a barrier layer which acts as a thermalinsulator, preventing, reducing or otherwise limiting the transfer ofheat from one device component to another or from a device component toan external structure, fluid or material. Useful thermal barriersinclude those comprising materials having a thermal conductivity of 0.3W/m·K or less, such as selected over the range of 0.001 to 0.3 W/m·K. Insome embodiments, a thermal barrier comprises active cooling components,such as components known in the art of thermal management. Thermalbarriers also include those barriers comprising thermal managementstructures, such as structures useful for transporting heat away from aportion of a device or tissue; in these and other embodiments, a thermalbarrier comprises thermally conductive material, for example materialhaving a high thermal conductivity, such as a thermal conductivitycharacteristic of a metal.

A barrier layer, and optionally a sacrificial layer on a substrate, maybe etched to produce a “mesh structure”, where at least a portion of thebarrier layer(s), and optionally the sacrificial layer on a substrate,is removed. For example a portion of the barrier layer(s) disposedapproximately 10 nm or more from an inorganic semiconductor component oradditional component is removed. Removal of at least a portion of thebarrier layer(s), and optionally the sacrificial layer on the substrate,may produce (i) one or more holes within the barrier layer(s) and/or(ii) electrical components, which are physically joined by a barrierlayer(s) at a proximal end and physically separated at a distal end. Inone embodiment, a mesh structure may be disposed upon a contiguousbioresorbable substrate, which provides structural support for thedevice during deployment into a biological environment.

“Contiguous” refers to materials or layers that are touching orconnected throughout in an unbroken sequence. In one embodiment, acontiguous layer of a biomedical device has not been etched to remove asubstantial portion (e.g., 10% or more) of the originally providedmaterial or layer.

“Biocompatible” refers to a material that does not elicit animmunological rejection or detrimental effect when it is disposed withinan in-vivo biological environment. For example, a biological markerindicative of an immune response changes less than 10%, or less than20%, or less than 25%, or less than 40%, or less than 50% from abaseline value when a biocompatible material is implanted into a humanor animal.

“Bioinert” refers to a material that does not elicit an immune responsefrom a human or animal when it is disposed within an in-vivo biologicalenvironment. For example, a biological marker indicative of an immuneresponse remains substantially constant (plus or minus 5% of a baselinevalue) when a bioinert material is implanted into a human or animal.

“Bioresorbable” refers to a material that is susceptible to beingchemically broken down into lower molecular weight chemical moieties byreagents that are naturally present in a biological environment. In anin-vivo application, the chemical moieties may be assimilated into humanor animal tissue. A bioresorbable material that is “substantiallycompletely” resorbed is highly resorbed (e.g., 95% resorbed, or 98%resorbed, or 99% resorbed, or 99.9% resorbed, or 99.99% resorbed), butnot completely (i.e., 100%) resorbed.

“Nanostructured surface” and “microstructured surface” refer to devicesurfaces having nanometer-sized and micrometer-sized relief features,respectively. Such structured surfaces are useful, for example, forcontacting and penetrating a target tissue and improving adhesionbetween the implantable biomedical device and the target tissue. Therelief features extend a length, x, from a substantially contiguousplane of the device surface. Quantitative descriptors of a structuredcontact surface include surface roughness parameters, such as R_(max),R_(a), and normalized roughness (R_(a)/R_(max)), all of which may bemeasured by atomic force microscopy (AFM). Rmax is the maximum heightbetween a highest peak to a lowest valley. Ra is the center-line-meanroughness, which is the average of an absolute value of a deviation froma center line of a roughness curve to the roughness curve. The surfaceof a substrate or barrier layer is “substantially smooth”, for thepurposes of this disclosure, if the surface has an R_(a) value of 100 nmor less. If the surface has an R_(a) value greater than 100 nm, thesurface is considered to be a “structured surface” for purposes of thisdisclosure. A structured surface may contain at least one featureselected from the group consisting of barbs, spikes, protrusions and anycombination of these.

“Accommodate” and “accommodation” refer to the configuration of onesurface or device to match the contours or relief features of anothersurface or device such that the two surfaces/devices are in intimatecontact. In one embodiment, a surface which accommodates a device ordevice component is a microstructured or nanostructured surface havingrelief features which match the shape, contours and or dimensions of thedevice or device component.

“Leakage current” or “leakage” refers to electric current which flowsfrom an electronic device along an unintended path. Under certainconditions, leakage of sufficient current from an electronic device candamage the device and/or components thereof. In certain circumstances,leakage current can also or alternatively damage the material into whichit flows.

“Active circuit” and “active circuitry” refers to one or more devicecomponents configured for performing a specific function. Useful activecircuits include, but are not limited to, amplifier circuits,multiplexing circuits, integrated circuits and current limitingcircuits. Useful active circuit elements include, but are not limitedto, transistor elements and diode elements.

“Permeability” refers to a property of a material such that one or moresubstances are able to pass through the material. “Selectivelypermeable” refers to a property of a material to allow certainsubstances to pass through the material while preventing othersubstances from being passed through. In one embodiment, a selectivelypermeable material allows one or more target chemicals, molecules and/orbiomolecules to be passed through the material while preventing water,salt and other substances from being passed through the material. In anembodiment, the barrier layer of a device has spatially patternedpermeable regions, impermeable regions or a combination of bothpermeable regions and impermeable regions.

The term “micro-scale” refers devices or device component having amaximum dimension (e.g., length, width, height, thickness, diameter,etc.) of 1000 μm. As used herein, the term micro-scale is intended todistinguish between objects having dimensions of cm to m and thosehaving dimensions of nm to μm. Micro-scale also refers, in someembodiments, to structures that are made using techniques known in theart of microfabrication.

“Plasmonic crystal” refers to an ordered array of micro- or nano-scaleelements which interact with electromagnetic radiation in an enhancedway due to the array structure. U.S. Pat. No. 7,705,280, herebyincorporated by reference, discloses useful plasmonic crystals andmethods for making plasmonic crystals.

“Suture” refers to a biomedical device used in the field of medicalsurgery. In embodiments, a suture is used in a medical procedure toclose an opening, wound or surgical incision in a tissue.

“Tensile strength” refers to an ability of a material to resist strainwithout undergoing fracture, damage or inelastic deformation.

“Young's modulus” refers to a mechanical property of a material, deviceor layer which refers to the ratio of stress to strain for a givensubstance. Young's modulus may be provided by the expression;

$E = {\frac{({stress})}{({strain})} = \left( {\frac{L_{0}}{\Delta\; L} \times \frac{F}{A}} \right)}$where E is Young's modulus, L₀ is the equilibrium length, ΔL is thelength change under the applied stress, F is the force applied and A isthe area over which the force is applied. Young's modulus may also beexpressed in terms of Lame constants via the equation:

$E = \frac{\mu\left( {{3\lambda} + {2\mu}} \right)}{\lambda + \mu}$where μ and λ are Lame constants. High Young's modulus (or “highmodulus”) and low Young's modulus (or “low modulus”) are relativedescriptors of the magnitude of Young's modulus in a given material,layer or device. In the present description, a High Young's modulus islarger than a low Young's modulus, about 10 times larger for someapplications, more preferably about 100 times larger for otherapplications and even more preferably about 1000 times larger for yetother applications.

“Bending stiffness” is a mechanical property of a material, device orlayer describing the resistance of the material, device or layer to anapplied bending moment. Generally, bending stiffness is defined as theproduct of the modulus and area moment of inertia of the material,device or layer. A material having an inhomogeneous bending stiffnessmay optionally be described in terms of a “bulk” or “average” bendingstiffness for the entire layer of material.

Described herein are flexible and stretchable semiconductor elementarrays and methods utilizing flexible and stretchable semiconductorelement arrays. Co-integration of flexible LED arrays with flexibleplasmonic crystals is useful for construction of fluid monitors,permitting sensitive detection of fluid refractive index andcomposition. Co-integration of flexible LED arrays with flexiblephotodetector arrays is useful for construction of flexible proximitysensors. Application of stretchable LED arrays onto flexible threads aslight emitting sutures provides novel means for performing radiationtherapy on wounds. Radiation therapy is also achievable usingbiocompatible or bioinert encapsulation over stretchable LED arrays forimplantation into biological tissues.

FIG. 1A provides a side plan view of a biomedical device 5 in abiological environment comprising a suture-mounted stretchable orflexible electronic circuit. The biomedical device comprises a suture 10having an external surface 20 and an optional stretchable or flexiblesubstrate 30 provided on at least a portion of the external surface ofthe suture 10. The suture may comprise any suitable material, such as afiber or thread, among others, particularly materials having mechanicalproperties (e.g., tensile strength, Young's modulus, etc.) and chemicalproperties (e.g., biocompatibility, bioinertness, etc.) useful for adesired application such as connecting tissue, therapy and/or diagnosis.In some embodiments, the suture 10 is a bioresorbable material, such assilk, and/or substrate 30 is a bioresorbable material, such as silk.

The biomedical device also comprises a stretchable or flexibleelectronic circuit 40 comprising inorganic semiconductor elements 41connected by stretchable or flexible conducting elements 45. In anembodiment, for example, stretchable or flexible electronic circuit 40comprises an array of electronic devices (e.g., LED array, electrodearray, transistors, multiplexer circuit, etc.), one or more sensors(e.g., optical sensors, chemical sensors, thermal sensors, etc.) and/ora drug delivery system. The flexible or stretchable electronic circuitis at least partially encapsulated in one or more barrier layers 50,which in some embodiments is a moisture barrier that prevents fluids(e.g., water, biological fluid, blood, ionic solution, etc.) from thebiological environment from contacting at least a portion of thestretchable or flexible electronic circuit. In some embodiments, the oneor more barrier layers 50 are a bioresorbable material, such as silk. Inan embodiment, barrier layer 50 has an external surface in contact withthe biological environment that is microstructured or nanostructured 55,for example, having one or more channels, vias, trenches, apertures,etc. In an embodiment, the composition, physical dimensions andmechanical properties of substrate 30, stretchable or flexibleelectronic circuit 40, barrier layer 50 are selected such thatstretchable or flexible electronic circuit 40 is provided proximate tothe neutral mechanical surface 51 of this combination of components(note: the neutral mechanical surface is shown schematically as dottedline 51).

Optionally, stretchable or flexible electronic circuit 40 furthercomprises one or more electrodes 46 positioned on the surface of barrierlayer 50 for establishing electrical contact with the biologicalenvironment and/or tissue. Electrodes may be in electrical contact withinorganic semiconductor elements of the electronic device 40 and may bepresent on an external surface 52 of barrier layer 50, and optionallypresent in a micro- or nanostructured feature 55 on external surface 52,such as in a channel, pore or via. The biomedical device can optionallybe connected to a controller 60 for controlling the stretchable orflexible electronic circuit. The controller 60 can be in wired orwireless, one-way or two-way communication with the stretchable orflexible electronic circuit using wired or wireless communication line70. In an embodiment, the controller 60 controls functionality of thestretchable or flexible electronic circuit such as sensing, thermalcontrol, electromagnetic radiation generation and detection, drugdelivery, among others.

FIG. 1B provides a side plan view of a biomedical device 5 comprising anoptical sensor device mounted on the outer surface 20 of a suture 10having a flexible or stretchable LED array 500 and a flexible orstretchable photodetector (PD) array 710, both of which are encapsulatedin one or more barrier layers 50, such as one or more low modulus (e.g.,less than or equal to 1 MPa) elastomeric layers. In an embodiment,barrier layer 50 functions as a moisture barrier to prevent transport ofwater, biological fluids, ionic solutions, soapy water, etc. to theflexible or stretchable LED array 500 and the flexible or stretchablephotodetector array 710 components of the optical sensor device 5. Theflexible or stretchable LED array 500 is comprised of LED islandstructures (schematically illustrated in FIG. 1B as rounded rectangles)and electrically conducting bridge structures (schematically illustratedin FIG. 1B as wavy lines). The flexible or stretchable photodetectorarray 710 is comprised of photodiode island structures (schematicallyillustrated in FIG. 1B as circles) and electrically conducting bridgestructures (schematically illustrated in FIG. 1B as wavy lines). Theflexible or stretchable LED array 500 and flexible or stretchablephotodetector array 710 are disposed on an optional flexible orstretchable substrate 30 which is disposed on the surface of suture 20.

The optical sensor device comprising a flexible or stretchable LED array500 and a flexible or stretchable photodetector array 710 is optionallyconnected to a controller 60 by wired or wireless, one-way or two waycommunication line 70. In an optical sensing embodiment, the controlleractivates the LED array 500 to produce electromagnetic radiation 730within a tissue environment 706. A portion of the electromagneticradiation reflected, scattered or emitted 740 by the tissue environment706 is incident on, and detected by, the photodetector array 710, forexample to provide a measurement of the chemical or physical propertiesof the tissue and/or biological environment.

In an embodiment, optical sensor device 5 has a composition, physicaldimensions and mechanical properties such that it can establishconformal contact with the nonplanar external surface of the suture 10.In an embodiment, for example, optical sensor device 5 is mounted on thecurved external surface 20 of the suture 10. In an embodiment, thecomposition, physical dimensions and mechanical properties of a flexibleor stretchable substrate 30, flexible or stretchable LED array 500,flexible or stretchable photodetector array 710, and barrier layers 50are selected such that flexible or stretchable LED array 500 and aflexible or stretchable photodetector array 710 are provided proximateto the neutral mechanical surface 703 of this combination of components(note: the neutral mechanical surface is shown schematically as dottedline 703).

In operation, the LED array 500 produces electromagnetic radiation 730,optionally having a selected intensity distribution as a function ofwavelength, which propagates away from optical sensor device 701. Forsome applications, the electromagnetic radiation 730 has wavelengths inthe visible or near infrared regions of the electromagnetic spectrum. Aportion of the electromagnetic radiation 730 from LED array 500interacts with objects in the tissue environment 706, resulting ingeneration of reflected, scattered and/or emitted electromagneticradiation 740 at various positions 705 within the tissue environment706. At least a portion of the reflected, scattered and/or emittedelectromagnetic radiation 740 is detected by photodetector array 710. Bymonitoring the intensity, wavelength distribution and/or radiant powerof the reflected, scattered and/or emitted electromagnetic radiation740, certain properties of the objects can be sensed and/or monitored,including composition and physical properties of the tissue inconnection with a therapy and/or diagnostic procedure.

FIGS. 1C and 1D provides a side plan view of a biomedical device 5comprising a drug delivery device on an optional flexible or stretchablesubstrate 30 mounted on the outer surface 20 of a suture 10 having anoptional temperature sensor 100, a resistive heater 110, such as asemiconductor resistive heater, and a drug-containing region 120, all ofwhich are encapsulated in one or more barrier layers 50, such as one ormore low modulus (e.g., less than or equal to 1 MPa) elastomeric layers.In FIGS. 1C and 1D, the pharmaceutical composition initially containedin the drug-containing region 120 is represented schematically as blackdots. In an embodiment, barrier layer 50 functions as a moisture barrierto prevent transport of water, biological fluids, ionic solutions, soapywater, etc. to the temperature sensor 100, resistive heater 110, anddrug-containing region 120. The resistive heater 110 can be a coilstructure, such as a thermistor, which is heated by passing currentthrough the coil region, thereby creating heat. In an embodiment, thecomposition, physical dimensions and mechanical properties of substrate30, temperature sensor 100, resistive heater 110, and drug-containingregion 120 are selected such that temperature sensor 100, resistiveheater 110, and drug-containing region 120 are provided proximate to theneutral mechanical surface 51 of this combination of components (note:the neutral mechanical surface is shown schematically as dotted line51).

The suture-mounted drug delivery device comprising an optionaltemperature sensor 100, a resistive heater 110, and a drug-containingregion 120 is optionally connected to a controller 60 by wired orwireless, one-way or two way communication line 70. In a drug deliveryembodiment, the controller activates the resistive heater 110 to produceheat which melts, degrades or otherwise renders porous, at least aportion of the barrier layer 50. In an embodiment, the controller 60monitors the output of the temperature sensor 100 and controls thesemiconductor heater 110 in order to melt or otherwise degrade thebarrier layer 50.

In an embodiment, suture-mounted drug delivery device 5 has acomposition, physical dimensions and mechanical properties such that itcan establish conformal contact with the nonplanar external surface ofthe suture 10. In an embodiment, for example, suture-mounted drugdelivery device 5 is mounted on the curved external surface 20 of thesuture 10. In an embodiment, the composition, physical dimensions andmechanical properties of a flexible or stretchable substrate 30,optional temperature sensor 100, resistive heater 110, drug-containingregion 120, and barrier layer 50 are selected such that optionaltemperature sensor 100, resistive heater 110, and drug-containing region120 are provided proximate to the neutral mechanical surface 51 of thiscombination of components (note: the neutral mechanical surface is shownschematically as dotted line 51).

The device before drug delivery is shown in FIG. 1C. As shown in FIG.1D, in operation the resistive heater 110 produces heat which melts atleast a portion of the barrier layer 30 which releases at least aportion of the pharmaceutical composition from the drug containingregion 120, resulting in release of the pharmaceutical composition 130to the tissue and/or biological environment. For some applications, theoptional temperature sensor 100 is used to monitor the temperaturechange produced by the resistive heater 110 to ensure that sufficientheat is created to melt at least a portion of the barrier layer 50 andto ensure that the heat generated does not substantially damage anysurrounding tissue or impair the function of the suture 10 orsuture-mounted drug delivery device 5.

FIG. 1E-F provides a side plan view of a biomedical device 5 comprisinga drug delivery device mounted on the outer surface 20 of a suture 10having a flexible or stretchable LED array 500, a flexible orstretchable photodetector (PD) array 710, and a drug-containing region120 all of which are encapsulated in one or more barrier layers 50, suchas one or more low modulus (e.g., less than or equal to 1 MPa)elastomeric layers. In an embodiment, barrier layer 50 functions as amoisture barrier to prevent transport of water, biological fluids, ionicsolutions, soapy water, etc. to the flexible or stretchable LED array500, the flexible or stretchable photodetector array 710, anddrug-containing region 120 components of the suture-mounted drugdelivery device 5. The flexible or stretchable LED array 500 iscomprised of LED island structures (schematically illustrated in FIG.1E-F as rounded rectangles) and electrically conducting bridgestructures (schematically illustrated in FIG. 1E-F as wavy lines). Theflexible or stretchable photodetector array 710 is comprised ofphotodiode island structures (schematically illustrated in FIG. 1E-F ascircles) and electrically conducting bridge structures (schematicallyillustrated in FIG. 1E-F as wavy lines). The flexible or stretchable LEDarray 500 and flexible or stretchable photodetector array 710 aredisposed on an optional flexible or stretchable substrate 30 which isdisposed on the surface of suture 20.

The suture-mounted drug delivery device comprising a flexible orstretchable LED array 500 and a flexible or stretchable photodetectorarray 710 is optionally connected to a controller 60 by wired orwireless, one-way or two way communication line 70. In a suture deliveryembodiment, the controller activates the LED array 500 to produceelectromagnetic radiation 730. A portion of the electromagneticradiation 730 is incident on the photodetector array 710 and is detectedby the controller 60.

In an embodiment, suture-mounted drug delivery device 5 has acomposition, physical dimensions and mechanical properties such that itcan establish conformal contact with the nonplanar external surface ofthe suture 10. In an embodiment, for example, optical sensor device 5 ismounted on the curved external surface 20 of the suture 10. In anembodiment, the composition, physical dimensions and mechanicalproperties of a flexible or stretchable substrate 30, flexible orstretchable LED array 500, flexible or stretchable photodetector array710, and barrier layers 50 are selected such that flexible orstretchable LED array 500 and a flexible or stretchable photodetectorarray 710 are provided proximate to the neutral mechanical surface 51 ofthis combination of components (note: the neutral mechanical surface isshown schematically as dotted line 51).

The device before drug delivery is shown in FIG. 1E. As shown in FIG.1F, in operation, the LED array 500 produces electromagnetic radiation730, optionally having a selected intensity distribution as a functionof wavelength, which photolytically degrades, or otherwise rendersporous, the barrier layer 30 sufficient to release at least a portion ofthe pharmaceutical composition from the drug containing region 120,resulting in release of the pharmaceutical composition 130 to the tissueand/or biological environment. For some applications, theelectromagnetic radiation 730 has wavelengths in the visible or nearinfrared regions of the electromagnetic spectrum. In an embodiment, aportion of the electromagnetic radiation 730 from LED array 500 isdetected by photodetector array 710, thereby providing a means formonitoring the drug delivery process. For example, by monitoring theintensity, wavelength distribution and/or radiant power ofelectromagnetic radiation 730 from LED array 500, certain properties ofthe released pharmaceutical composition 120 can be determined, includingthe rate of delivery and relative amount of released pharmaceuticalcomposition 120.

FIG. 2 provides a top plan view of a biomedical device 5 in a biologicalenvironment comprising a suture-mounted stretchable or flexibleelectronic circuit wherein the suture 10 closes a wound 210 in a tissue200. The elements of the flexible or stretchable electronic circuit 40are disposed on the surface of the suture 10. In this configuration thesuture 10 can be used for closing the wound 210, for example, by sewingor stitching together tissue. In some embodiments, the stretchable orflexible electronic circuit 40 of the biomedical device 5 supportsadvanced diagnostic and/or therapeutic functionality, such providingoptical emission allowing for visualization of suture 10 or enablingdrug delivery or delivery of electromagnetic radiation to the wound 210or tissue 200. In some embodiments, the stretchable or flexibleelectronic circuit 40 of the biomedical device 5 supports sensingfunctionality such as measuring the temperature and/or chemical orphysical properties of wound 210 or tissue 200, and/or measuring theamount of a therapeutic agent provided to the wound 210 or tissue 200 asa function of time. In some embodiments, biomedical device 5 comprisesbioresorbable materials and, thus, is capable of being at leastpartially resorbed upon making contact with the tissue 200 in thebiological environment. In some embodiments, biomedical device 5 has acomposition and physical dimensions such that it can be removed fromcontact with tissue 200 after treatment and/or diagnosis of tissue 200in the biological environment.

FIG. 3 provides a top plan view of a portion of an example of abiomedical device 5 comprising a suture-mounted stretchable or flexibleelectronic circuit. Semiconductor elements 41 are disposed on thesurface of the suture 10 and are connected by stretchable or flexibleconducting elements 45. The biomedical device can optionally beconnected to a controller 60 for controlling the stretchable or flexibleelectronic circuit. The controller 60 can be in wired or wireless,one-way or two-way communication with the stretchable or flexibleelectronic circuit using wired or wireless communication line 70. Thecontroller 60 can control functions of the stretchable or flexibleelectronic circuit such as imaging, drug delivery, electromagneticradiation delivery and detection, among others.

FIG. 4A-E provides a schematic showing various approaches for creatinglayers of flexible or stretchable electronic circuits 401 optionallyprovided in a multilayer laminated geometry. FIG. 4A provides a sideplan view of a flexible or stretchable electronic circuit 401 comprisingan array of electronically interconnected island 400 and bridge 410structures. The island structures 400 may comprise inorganicsemiconductor elements, such as semiconductor-based devices and devicearrays, such as LEDs, transistors, lasers, photodetectors, multiplexcircuitry, logic circuitry, etc. The bridge structures 410 may becomprised of conductive material, such as a metal, and optionally areprovided in a serpentine configuration between the island 400structures, and optionally encapsulated by a low modulus elastomerlayer. In some embodiments, the length and configuration (e.g.,serpentine, bent, wavy, buckled, etc.) of bridge structures 410 providesoverall device flexibility and/or stretchability for a range ofapplications. The array 401 of electronically interconnected island 400and bridge 410 structures may be at least partially encapsulated in abarrier layer, and in some embodiments are completely encapsulated in abarrier layer. FIG. 4B-E provide side plan views of stackedconfigurations 402 of stretchable or flexible electronic circuitsprovided in a multilayer geometry wherein the layers are connected by anadhesive 420 (FIG. 4B), directly connected (FIG. 4C), connected by aflexible or stretchable substrate 30 (FIG. 4D), and connected byflexible or stretchable substrates 30 and adhesive 420 (FIG. 4E). Asshown in FIG. 4B, an array of electronically interconnected island 400and bridge 410 structures is provided in a multilayered geometryconnected by an adhesive layer 420 and is optionally provided on aflexible or stretchable substrate 35. As shown in FIG. 4C, an array ofelectronically interconnected island 400 and bridge 410 structures isprovided in a multilayered geometry wherein the stacked arrays areprovided in direct contact and are optionally provided on a flexible orstretchable substrate 35. As shown in FIG. 4D, an array ofelectronically interconnected island 400 and bridge 410 structures isprovided in a multilayered geometry connected by a flexible andstretchable substrate 30 and is optionally provided on a flexible orstretchable substrate 35. As shown in FIG. 4E, an array ofelectronically interconnected island 400 and bridge 410 structures isprovided in a multilayered geometry connected by flexible or stretchablesubstrates 30 and an adhesive layer 420, and is optionally provided on aflexible or stretchable substrate 35.

A device as described herein can contain many arrays 401 ofelectronically interconnected island 400 and bridge 410 structuresprovided in stacked configurations 402 as set forth in FIG. 4A-E, or anycombination of the stacked configurations 402 as set forth in FIG. 4A-E.In an embodiment, for example, a device as described herein comprises aplurality of arrays 401 of electronically interconnected island 400 andbridge 410 structures provided in stacked configurations 402 connectedby adhesive 420 and a plurality of arrays 401 of electronicallyinterconnected island 400 and bridge 410 structures provided in stackedconfigurations 402 connected by a flexible or stretchable substrate 30.

The multilayered stacked geometries of the arrays 401 of electronicallyinterconnected island 400 and bridge 410 structures shown in FIG. 4A-Ecan be encapsulated in various configurations, for example in amultilayer laminated geometry. FIG. 4F-H provides a schematic showingvarious approaches for creating stacked layers of flexible orstretchable electronic circuits 402. FIGS. 4F-H provide side plan viewsof stacked configurations of stretchable or flexible electronic circuits402 wherein the individual layers are connected by an encapsulationlayer 405 (FIG. 4F), lamination of encapsulated layers 405 (FIG. 4H),and printing of electronically interconnected island 400 and bridge 410structures on a laminated layer 405 (FIG. 4H). The encapsulation layer405 can serve as a surface for lamination (as shown in FIG. 4G) or asurface for molding one or more additional components, such as opticalcomponents (e.g., lens arrays, filters, diffusers, etc.) or drugdelivery components (e.g., encapsulated pharmaceutical compositions).Additionally, the encapsulation layer 405 may provide for electronicisolation for a least a portion of the arrays 401 of electronicallyinterconnected island 400 and bridge 410 structures from a biologicalenvironment and/or may additionally serve as a moister barrier from abiological environment. In addition to serving as an electronic and/ormoisture barrier layer, the encapsulation layer 405 can also serve toprovide mechanical stability to the arrays 401 of electronicallyinterconnected island 400 and bridge 410 structures. In an embodiment ofthat shown in FIG. 4F, the encapsulation layer 405 is a laminate layer.In a further embodiment of that shown in FIG. 4F, the encapsulationlayer 405 has mechanical properties chosen so as to allow for stretchingor flexing of the stretchable or flexible electronic circuit withoutcausing damage to the circuit or encapsulation layer 405. In anembodiment of that shown in FIG. 4H, the electronically interconnectedisland 400 and bridge 410 structures are provided on the encapsulationlayer 405, for example, by a printing process, such as a dry transfercontact printing technique.

FIGS. 4I-4U provide schematic diagrams of strategies to create opticalelements on a laminated flexible or stretchable electronic circuit 455,including lenses 485 (FIG. 4I-4K), diffusers 486 (4L-4N), reflectivecoatings 487 (40-4P), reflective coatings 487 having a transparentsection 489 (4Q-4R), and a micro- or nanostructured grating 490 (4S-4U).In FIG. 4I-4K, the strategy includes providing an array 403 of island400 and bridge 410 structures contained in an encapsulation layer 405,as shown in FIG. 4I. The array 403 is then coated with a moldable layer480, such as a prepolymer, as shown in FIG. 4J. The moldable layer 480is then contacted by a pattern transfer device 495, such as a mold orstamp, to form lenses 485 on the encapsulation layer 405, as shown inFIG. 4K. In FIG. 4L-4N, the strategy includes providing an array 403 ofisland 400 and bridge 410 structures contained in an encapsulation layer405, as shown in FIG. 4L. The array 403 is then coated with a moldablelayer 486 comprising diffusive elements shown as black dots, such as aprepolymer, as shown in FIG. 4M. The moldable layer 486 is thencontacted by a pattern transfer device 495, such as a mold or stamp, toform diffusive lenses 487 on the encapsulation layer 405, as shown inFIG. 4N. In FIG. 4O-P, the strategy includes providing an array 403 ofisland 400 and bridge 410 structures contained in encapsulation layer405, as shown in FIG. 4O. The array 403 is then coated with a reflectivecoating layer 488, as shown in FIG. 4P. The reflective coating layer 488can be, for example, an antireflective coating layer, a partiallyreflecting layer, or an optical filter layer. In FIG. 4Q-4R, thestrategy includes providing an array 403 of island 400 and bridge 410structures contained in an encapsulation layer 405, as shown in FIG. 4Q.The array 403 is then coated with a reflective coating layer 488 havinga window region 489, as shown in FIG. 4R. The reflective coating layer488 can be, for example, an antireflective coating layer, a partiallyreflecting layer, or an optical filter layer. In FIG. 4S-T, the strategyincludes providing an array 403 of island 400 and bridge 410 structurescontained in an encapsulation layer 405, as shown in FIG. 4S. The array403 is then coated with a moldable layer 480, such as a prepolymer, asshown in FIG. 4T. The moldable layer 480 is then processed to form amicro- or nanostructure 490 on the barrier layer laminate 405, as shownin FIG. 4U. The micro- or nanostructure 490 can be, for example, agrating or photonic crystal.

In some embodiments, individually encapsulated arrays of electronicallyinterconnected island 400 and bridge 410 structures, such asindividually encapsulated LED arrays, are provided in a multilayerstacked device geometry to form three dimensional arrays ofelectronically interconnected island 400 and bridge 410 structures. Suchmultilayer device geometries are particularly beneficial for providinghigh density arrays of inorganic light emitting diodes (ILEDS) capableof providing radiant intensities and powers useful for biomedicalapplications. An example, of a three dimensional array of ILEDS isexemplified in FIG. 5A which provides a side plan view of offset andstacked arrays of flexible or stretchable ILED arrays while FIG. 5Bprovides a top plan view of the same offset and stacked arrays offlexible or stretchable ILED arrays. As shown in FIG. 5B, offset stacksof individual 2D arrays of electronically interconnected island 400 andbridge 410 structures provides very high two dimensional density ofelectronically interconnected island 400 and bridge 410 structures,while at the same time maintaining a high degree of flexibility and/orstretchability. This configuration is especially useful in imaging,sensing, and phototherapy applications wherein at least a portion of thethree dimensional stacked arrays of electronically interconnected island400 and bridge 410 structures comprise ILEDs for generationelectromagnetic radiation and/or wherein at least a portion of the threedimensional stacked arrays of electronically interconnected island 400and bridge 410 structures comprise photodiodes for detectingelectromagnetic radiation. LED arrays useful in this aspect includemultilayer structures comprising a plurality of individuallyencapsulated LED arrays provided in a laminated device configuration.

FIG. 6 provides a side plan view of a fluid delivery monitor device 601comprising a flexible or stretchable electronic circuit. The fluiddelivery monitor device 601 comprises a tube 602 for delivery of fluidhaving an outer wall 600 for containing a fluid having a flow directionindicated by arrow 640. The fluid delivery monitor device furthercomprises a plasmonic crystal 610 disposed within or on the tube wall600 and in fluid communication with the fluid in the tube 602. Photoniccrystal has sensing surface 611 provided in physical contact with fluidin tube 602. In an embodiment, sensing surface comprises: (1) asubstrate having a first surface with a plurality of features 612provided in a first array and (2) one or more films 613 comprising anelectrically conductive material, wherein at least a portion of the oneor more films 613 is supported by the first surface, and wherein atleast a portion of the one or more of the films 613 comprise theelectrically conducting material is spatially aligned with each of thefeatures 612 of the first surface. In an embodiment, the substratehaving the first surface with a plurality of features 612 comprises ananoimprinted or replica-molded structure.

In some embodiments, plasmonic crystal 610 is a molded or embossedstructure, and optionally is molded or embossed on the inner surface ofthe tube 602 to provide access of the sensing surface to the fluid inthe tube 602. Alternatively, plasmonic crystal 610 is disposed in anaperture in tube 602 to provide access of the sensing surface to thefluid in the tube 602. In optical communication with the plasmoniccrystal 610 and tube 602 is an array of electronically interconnectedisland 400 and bridge 410 structures encapsulated in a barrier layer 50,wherein the island structures are LEDs, for example provided in a 2D LEDarray or 3D LED array. In an embodiment, for example, array ofelectronically interconnected island 400 and bridge 410 structures is amultilayer structure comprising a plurality of individually encapsulatedLED arrays. In the configuration shown in FIG. 6, an optional flexibleor stretchable substrate 620 is disposed between the plasmonic crystal610 and the array of electronically interconnected island 400 and bridge410 structures. In some embodiments, plasmonic crystal 610 is inphysical contact with the LED array or alternatively is in physicalcontact with optional substrate 610 provided between the plasmoniccrystal and the LED array. Alternatively, the plasmonic crystal 610 ismolded on a surface of a LED array. In an embodiment, the composition,physical dimensions and mechanical properties of flexible or stretchablesubstrate 620, array of electronically interconnected island 400 andbridge 410 structures and barrier layer 50 are selected such that arrayof electronically interconnected island 400 and bridge 410 structures isprovided proximate to the neutral mechanical surface 602 of thiscombination of components (note: the neutral mechanical surface is showschematically as dotted line 602).

In some embodiments, plasmonic crystal 610, LED array and optionalsubstrate 610 are provided in a laminated device geometry. In someembodiments, plasmonic crystal 610, LED array and optional substrate 620are each flexible device components capable of efficient integrationwith tube 602, e.g., able to assume a nonplanar (e.g., curvedconfiguration or bent configuration).

The fluid delivery monitoring device 601 of FIG. 6 also comprises adetector 630 positioned on an outer wall 600 of the tube. Detector 630is in optical communication with plasmonic crystal 610, and ispositioned for detecting electromagnetic radiation produced by the LEDisland structures 400 and transmitted by plasmonic crystal 610. In anembodiment, for example, detector 630 is a flexible and/or stretchablephotodetector or array of photodetectors, such as an array of inorganicsemiconductor-based photodetectors. As shown in FIG. 6, the detector 630is in optical communication with plasmonic crystal 610 and the LEDarray. An optional controller 60 is also shown which is provided inwired or wireless communication with both the array of electronicallyinterconnected island 400 and bridge 410 structures and the detector630. The controller 60 is in one-way or two-way communication with thedetector 630 and the array of electronically interconnected island 400and bridge 410 structures by wired or wireless communication line 70.The controller 60 can control functions of the fluid delivery monitorsuch as imaging, drug delivery, and electromagnetic radiation deliveryand detection, among others.

In operation, the array of LEDs of the fluid delivery monitoring device601 generates electromagnetic radiation, at least a portion of which istransmitted through the plasmonic crystal 610 and detected by detector630. Interaction of the fluid in tube 602 and one or more exposedsensing surfaces of plasmonic crystal 610 establishes, in part, theoptical transmission properties of the plasmonic crystal 610, such asthe wavelengths of electromagnetic radiation transmitted by theplasmonic crystal and the percentage transmission of the plasmoniccrystal as function of wavelength. For example, the composition of thefluid determines the refractive index proximate to the external surfaceof the plasmonic crystal which significantly impacts the transmissionproperties. Therefore, by monitoring the intensity and/or wavelength oflight transmitted by plasmonic crystal 610, the composition of the fluidmay be monitored, for example, monitored as a function of time. In anembodiment, fluid delivery monitoring device 601 is a component of anintravenous delivery system and is useful for monitoring the amount of afluid component, such as a drug, biological materials (e.g., proteins,blood or a component thereof) or nutrient, administered to a patientundergoing treatment.

FIG. 7 provides a side plan view of an optical sensor device 701comprising a flexible or stretchable LED array 500 and a flexible orstretchable photodetector array 710, both of which are encapsulated inone or more barrier layers 50, such as one or more low modulus (e.g.,less than or equal to 1 MPa) elastomeric layers. In an embodiment,barrier layer 50 functions as a moisture barrier for prevent transportof water, biological fluids, ionic solutions, soapy water, etc. to theflexible or stretchable LED array 500 and the flexible or stretchablephotodetector array 710 components of the proximity sensor device 701.The flexible or stretchable LED array 500 comprises LED islandstructures (schematically illustrated in FIG. 7 as rounded rectangles)and electrically conducting bridge structures (schematically illustratedin FIG. 7 as wavy lines). The flexible or stretchable photodetectorarray 710 also comprises of photodiode island structures (schematicallyillustrated in FIG. 7 as circles) and electrically conducting bridgestructures (schematically illustrated in FIG. 7 as wavy lines). Theflexible or stretchable LED array 500 and flexible or stretchablephotodetector array 710 are disposed on an optional flexible orstretchable substrate 30 which is disposed on the surface of device 720,such as a surgical glove, a tools, a robotic device, among others.

The proximity sensor device comprising a flexible or stretchable LEDarray 500 and a flexible or stretchable photodetector array 710 isoptionally connected to a controller 60 by wired or wireless, one-way ortwo way communication line 70. In a proximity sensing embodiment, thecontroller activates the LED array 500 to produce electromagneticradiation 730 in the direction of the surface of an object 700,optionally in a biological environment. A portion of the electromagneticradiation reflected, scattered or emitted 740 by the object 700 isincident on the photodetector array 710 and is detected by thecontroller 60.

In an embodiment, proximity sensor device 701 has a composition,physical dimensions and mechanical properties such that it can establishconformal contact with the nonplanar external surface of a surgicaldevice. In an embodiment, for example, proximity sensor device 701 ismounted on the curved external surface of a surgical glove or surgicaltool. In an embodiment, for example, proximity sensor device 701 ismounted on the curved or planar external surface of a roboticmanipulator or a machine part. In an embodiment, the composition,physical dimensions and mechanical properties of a flexible orstretchable substrate, flexible or stretchable LED array 500, flexibleor stretchable photodetector array 710, and barrier layers 50 areselected such that flexible or stretchable LED array 500 and a flexibleor stretchable photodetector array 710 are provided proximate to theneutral mechanical surface 703 of this combination of components (note:the neutral mechanical surface is show schematically as dotted line703).

In operation, the LED array 500 produces electromagnetic radiation 730,optionally having a selected intensity distribution as a function ofwavelength, which propagates away from proximity sensor device 701. Forsome applications, the electromagnetic radiation 730 has wavelengths inthe visible or near infrared regions of the electromagnetic spectrum. Aportion of the electromagnetic radiation 730 from LED array 500interacts with an object 700, resulting in generation of reflected,scattered and/or emitted electromagnetic radiation 740. At least aportion of the reflected, scattered and/or emitted electromagneticradiation 740 is detected by photodetector array 710. By monitoring theintensity, wavelength distribution and/or radiant power of thereflected, scattered and/or emitted electromagnetic radiation 740,certain properties of the object can be sensed and/or monitored,including position and/or distance from the proximity sensor.

The flexible or stretchable waterproof electronics described herein areuseful in a diverse array of methods. FIG. 8 provides a flow diagram ofa wound treatment method employing a biomedical device comprising asuture having a flexible or stretchable LED array for exposing the woundto electromagnetic radiation. FIG. 9 provides a flow diagram of a methodof making a suture comprising roll printing or transfer printinginorganic semiconductor elements onto a flexible or stretchable threadand encapsulating the inorganic semiconductor elements with a barrierlayer. FIG. 10 provides a flow diagram of a method of treating a tissuein a biological environment comprising contacting the tissue with abiomedical device comprising a suture and a flexible or stretchableelectronic circuit. The tissue can be treated using many methods, suchas methods comprising exposure to electromagnetic radiation, closing awound in the tissue with a suture as described herein, actuating orsensing the tissue and/or wound, and release of a pharmaceuticalcomposition to the wound and/or tissue from the biomedical device, amongothers.

The invention may be further understood by the following non-limitingexamples.

EXAMPLE 1 Waterproof AlInGaP Optoelectronics on Flexible Tubing,Sutures, Gloves and Other Unusual Substrates, with Application Examplesin Biomedicine and Robotics

This example explores new areas and implements mechanically optimizedlayouts to achieve arrays of inorganic LEDs and PDs in systems that canaccommodate extreme modes of mechanical deformation, for integration onsubstrates of diverse materials and formats. Additionally, materials anddesign strategies allow operation even upon complete immersion in salinesolutions, biofluids, solutions of relevance to clinical medicine andsoapy water, thereby opening new and unconventional opportunities forseamless integration of optoelectronics with biomedical and roboticsystems. Light emitting sutures, thin implantable sheets (i.e. LEDtattoos) and balloon catheters, and flexible, optical proximity andrefractive index sensors provide some examples. Specifically, thisexample describes seven advances, in the following order: (1)experimental and theoretical aspects of mechanical designs that enablefreely deformable, interconnected collections of LEDs and PDs on soft,elastomeric membranes, bands and coatings, (2) strategies for achievinghigh effective fill factors in these systems, using laminated multilayerconstructs, (3) device examples on diverse substrates and in variedgeometrical forms, (4) low modulus, biocompatible encapsulationmaterials that preserve key mechanical properties and, at the same time,enable robust operation when integrated on or implanted in livingsystems, (5) flexible optoelectronic components for biomedicine, with invivo demonstrations on animal models, (6) illuminated plasmonic crystaldevices, as high performance refractive index monitors for intravenousdelivery systems and (7) waterproof optical proximity sensors that mounton the curved fingertips of vinyl gloves, for possible use in roboticsor advanced surgical devices.

For active materials, thin epitaxial semiconductor layers grown on GaAswafers are prepared, and then vertically etched to define lateraldimensions of devices built with them. Release from the wafer viaselective elimination of an underlying layer of AlAs, followed bytransfer printing accomplishes integration on substrates of interest.The fabrication scheme described here uses a dual transfer process thatinvolves first printing the semiconductor materials to a temporarysubstrate (glass plate coated with a trilayer of epoxy/polyimide(P1)/poly(methylmethacrylate) (PMMA)) for forming contacts,interconnections and structural bridges, and encapsulation layers.Dissolving the PMMA releases fully formed, interconnected collections ofdevices. A second transfer printing step achieves integration onelastomeric sheets (e.g. poly(dimethylsiloxane), PDMS) or othersubstrates coated with thin layers of PDMS, with strong bonding only atthe locations of the devices. For all examples described in thisexample, the LEDs (referred to herein as μ-ILEDs to highlight the smallsizes and the distinction over organic devices), and the PDs (i.e.μ-IPDs) have lateral dimensions of 100×100 μm and thicknesses of 2.5 μm,corresponding to volumes that are orders of magnitude smaller than thoseof commercially available devices. The thin geometries are importantbecause they allow the use of thin film metallization for interconnectand optimized mechanical designs, described next. Details of theprocessing and layouts appear in FIGS. 17-19.

FIGS. 11A and 20 present optical images, schematic illustrations,scanning electron microscope (SEM) images, and finite element modelingof the mechanics of arrays of μ-ILEDs connected by serpentine shapedribbons that serve as either structural bridges or electricalinterconnects, transferred to a thin, pre-strained sheet of PDMS (˜400μm thick). Here, and as described below, the devices are connected inseries (FIG. 18A), such that all of them turn on and off together; asingle failed device leads to failure of the entire array. Theinterconnects consist of thin films of metal with photodefined layers ofepoxy on top and bottom to locate the metal at the neutral mechanicalplane. The bridges are similar, but without the metal. Detailedgeometries appear in FIG. 19. Releasing the pre-strain yieldsnon-coplanar layouts in the serpentines via a controlled, non-linearbuckling response, as shown in the left frame of FIG. 11A (˜20%pre-strain). The right frame and inset of FIG. 11A present a schematicillustration and magnified optical image of a representative μ-ILED,respectively. These design choices are informed by careful studies ofthe mechanics through three dimensional finite element modeling (3D-FEM)of the complete systems; they represent highly optimized versions ofthose used for silicon circuits and μ-ILEDs. The results enable stableand robust operation during large scale uniaxial, biaxial, shear andother mixed modes of deformation, as described in the following.

FIGS. 20A and 21A show tilted view scanning electron microscope (SEM)images and corresponding optical microscope images of adjacent μ-ILEDsand non-coplanar serpentine interconnects formed with ˜20% biaxialpre-strain before (left) and after (right) uniaxial stretching (˜60%),respectively. The separations between adjacent pixels change by anamount expected from the pre-strain and the applied strain, where acombination of in- and out-of-plane conformational changes in theserpentines accommodate the resulting deformations in a way that avoidsany significant strains at the positions of the μ-ILEDs. In particular,3D-FEM modeling results (FIG. 20B) reveal peak strains in the metalinterconnect and the μ-ILEDs that are >300 times smaller than theapplied strain (FIG. 21C shows similar results for ˜59% stretching alongthe diagonal direction, corresponding to FIG. 21B). FIGS. 11B and 22present two dimensional, in-plane stretching of a 6×6 array of μ-ILEDsalong horizontal (left) and diagonal (right) directions. The uniform andconstant operating characteristics of all devices are clearly apparentin the dark and bright (without and with external illumination) imagesof FIG. 11B and FIG. 22 as well as in the current-voltage (I-V)characteristics (left frame of FIG. 11C). The applied strains,calculated from the separations of inner edges of adjacent pixels beforeand after stretching, reach ˜48% and ˜46% along the horizontal anddiagonal directions, respectively. The I-V characteristics are invarianteven after 100000 cycles of 75% stretching along the horizontaldirection (right frame of FIG. 11C).

Uniaxial stretching and compressing are among the simplest modes ofdeformation. Others of interest include biaxial, shear and related. Theresults of FIGS. 11D-G, and 23 demonstrate the ability of the reporteddesigns to allow these sorts of motions, through large strains inducedby pneumatic pressure, achieved by inflation of a thin (500 μm) membraneof PDMS that supports an array similar to that of FIG. 11B. Injectingair through a syringe in a specially designed cylinder that serves as amount for the device deforms the initially flat array (top frame of FIG.11D) into a balloon shape (bottom frame of FIG. 11D). FIG. 11E showsfour pixels in the ‘flat’ (top) and ‘inflated’ states (bottom) duringoperation, with external illumination. The area expansion induced inthis manner can reach ˜85% without any device failures. The I-Vcharacteristics also show no appreciable differences between the flatand inflated states (FIG. 11F). 3D-FEM is used to model the inflationinduced deformation of a circular elastomeric membrane, with the samethickness (500 μm) and diameter (20 mm) as in experiment, but without amounted μ-ILED array. As illustrated in FIGS. 11G and 23C, both thecircumferential and meridional strains reach ˜37.3% when inflated to aheight of 8.3 mm, the same as in the bottom frame of FIG. 11D. Measureddisplacements of devices in the system of the bottom frame of FIG. 11Eindicate strains of ˜36%, which are comparable to values calculated by3D-FEM. This observation suggests an important conclusion: with thedesigns reported here, the arrays provide negligible mechanical loadingof the soft, elastomeric membrane support, consistent with the very loweffective modulus provided by the optimized, non-coplanar serpentines.

Corkscrew twisting (FIG. 12A) provides another well-defined mode ofdeformation that is of interest. Here, large shear strains occur inaddition to stretching/compressing in the axial and width directions.The device test structure in this case consists of a 3×8 array ofμ-ILEDs transferred to a band of PDMS without pre-strain (see FIG. 24Afor details). Optical images of flat, 360°, and 720° twistingdeformations with (left) and without (right) external illumination (FIG.12A) reveal uniform and invariant emission. These strains lead toout-of-plane motions of the serpentines, as shown in FIGS. 12B and 24B.The μ-ILEDs remain attached to the PDMS substrate due to their strongbonding. Electrical measurements indicate similar I-V characteristicswith different twisting angles (FIG. 12C) and at different stages offatigue tests, as shown in FIG. 24C. FIG. 12D presents distributions ofvarious strain components, evaluated at the surface of a band of PDMSwith thickness 0.7 mm by 3D-FEM: axial stretching (left frame), widthstretching (middle frame) and shear (right frame). (For 360° twisting,see FIG. 25). The results demonstrate that the PDMS surface undergoesboth extreme axial/width stretching and shear deformations, with sheardominating, and reaching values of ˜40% for the 720° twist. As for thecase of FIGS. 11D and 11G, the distributions of strain for the bare PDMSsubstrate can provide reasonably good estimates for the system. Thesecontrolled uniaxial (FIG. 11B), biaxial (FIG. 11D) and twisting (FIG.12A) modes suggest an ability to accommodate arbitrary deformations. Astwo examples, FIGS. 12E and 12F show cases of stretching onto the sharptip of a pencil and wrapped onto a cotton swab. The array of 6×6 μ-ILEDspulled onto the pencil (red arrows indicate stretching directions)experiences local, peak strains of up to ˜100%, estimated from distancesbetween adjacent devices in this region. Similar but milder and morespatially distributed deformations occur on the cotton swab, with an 8×8array. In both cases, observation and measurement indicate invariantcharacteristics, without failures, even in fatigue tests (FIGS. 12G and26).

A feature of the layouts that enable these responses is the relativelysmall area coverage of active devices, such that the serpentinestructures can absorb most of the motions associated with appliedstrain. An associated disadvantage, for certain applications, is thatonly a small part of the overall system emits light. This limitation canbe circumvented with layouts that consist of multilayer stacks ofdevices, in laminated configurations, with suitable spatial offsetsbetween layers. The exploded view schematic illustration in FIG. 13Ashows this concept with four layers. FIG. 27 provides details.Integration is accomplished with thin coatings of PDMS (˜300 μm) thatserve simultaneously as elastomeric interlayer dielectrics, encapsulantsand adhesives. Here, each layer consists of a substrate of PDMS (300 μmthick) and an array of LEDs (total thickness with interconnect, ˜8 μm).The total thickness of the four layer system, including interlayers ofPDMS, is ˜1.3 mm. Optical images of emission from a four layer systemappear in FIG. 13B (with external illumination) and FIG. 27B (withoutexternal illumination). FIG. 13C shows a two layer case, where eachlayer lights up in a different pattern. The inset on the rightillustrates the same system in a bent state (bending radius=2 mm), wherethe maximum strain in top and bottom GaAs layers is only 0.006% and0.007%, respectively as shown by 3D-FEM simulation (FIG. 28). The PDMSinterlayers restrict the motion of the serpentines, but by an amountthat reduces only slightly the overall deformability. The extent of freemovement can be maximized by minimizing the modulus of the encapsulant.Here, PDMS was mixed in a ratio to yield a Young's modulus of ˜0.1 MPa,to retain nearly ˜90% of the stretchability of the unencapsulated case.

The favorable mechanical characteristics enable integration onto avariety of substrates that are incompatible with conventionaloptoelectronics. As demonstrations, μ-ILED devices were built onswatches of fabric (FIG. 29A), tree leaves (FIG. 29C), sheets of paper(FIG. 13D), pieces of aluminum foil (FIG. 13E) and balloon catheters(FIG. 13F). In all cases, transfer printing successfully delivers thedevices to these substrates with thin (˜50 μm) coatings of PDMS thatserve as planarizing and strain isolating layers, and as adhesives.Bending and folding tests for each case indicate robust operation underdeformed states. The smallest bending radii explored experimentally were4 mm, 2.5 mm, and 400 μm for the fabric, leaf, and paper, respectively.Theoretical modeling, using Young's moduli and thicknesses 1.2 MPa, 800μm, 23.5 MPa, 500 μm, 600 MPa and 200 μm for the fabric, leaf and paper,respectively, shows that the fabric, leaf and paper can be completelyfolded, in the sense that the strain in the GaAs remains much smallerthan its failure strain (˜1%) even when the bend radius equals thesubstrate thickness. Without the strain isolation provided by the PDMS,the fabric can still be folded, but the leaf and paper can only be bentto minimal radii of 1.3 mm and 3.5 mm, respectively. This result occursbecause the Young's modulus of PDMS (0.4 MPa) is much smaller than thoseof leaf and paper (i.e., strain isolation), while the Young's moduli ofPDMS and fabric are more similar. Random wrinkling, includingmulti-directional folding with inward and outward bending can beaccommodated, as is apparent in the devices on paper and aluminum foil(˜30 μm). In images of the latter case (FIG. 13E), the number density ofwrinkles reaches ˜200 per cm² with approximate radii of curvature assmall as 150 μm (See FIGS. 29-34 for additional images, plots of I-Vcharacteristics, results of fatigue tests, and surface topography ofthese substrates).

The arrays of μ-ILEDs mounted on the surface of an otherwiseconventional catheter balloon (FIG. 13F) enables highly localizedphotodynamic drug delivery to selectively treat a variety ofintraluminal tumors and cardiovascular disorders, includingatherosclerotic plaque lesions. Phototherapy (e.g., stabilization ofplaque) and spectroscopic characterization of arterial tissue representother uses. Thin threads and fibers represent other substrates ofbiomedical interest, due to their use as sutures and implants, asdescribed next. FIGS. 13G and 13H present images of an array of μ-ILEDs(1×8) with serpentine metal bridges and a single μ-ILED device with long(1.25 cm×185 μm) metal interconnects, both on flexible, thin (˜8 μm)ribbons mounted onto cylindrical supports. FIG. 13I shows relatedsystems, consisting of μ-ILED arrays on pieces of thread, and wrappedaround a rod and tied in a knot (inset). FIGS. 32A-C provide additionalimages with different thicknesses of conventional threads. Threads ofnylon (FIG. 13I) and cotton (FIGS. 32A-C) were explored, with diametersof ˜0.7 mm, ˜2.5 mm, and ˜0.7 mm, ˜0.3 mm, respectively. Integration onthese and other small substrates is challenging with the usualtechniques for transfer printing. Instead, threads were rolled over theglass carrier substrate in a manner that avoided the use of a separatetransfer stamp and the associated difficulties in alignment and contact(see FIGS. 32D-E). As clearly illustrated in FIG. 13I, the optimizedmechanical designs described previously enable these systems to betwisted, bent and tied into knots without affecting the operation, evenwhen encapsulated with PDMS. The approximate minimum bending radii formain and inset frame of FIG. 13I is ˜3 mm and ˜0.7 mm, respectively.

FIG. 14A demonstrates the use of a device like those in FIG. 13I as alight emitting suture in an animal model, manipulated with aconventional suture needle starting from the initial incision (upperleft) to the completion of three stitches (lower left; FIG. 32F shows anincised paper sheet sutured with a similar device, in a similar manner).The 1×4 array of μ-ILEDs in this case operates without any failures, duepartly to favorable mechanics as described previously but also to afully encapsulating layer of PDMS as a soft, elastomeric andbiocompatible barrier to the surrounding tissue and associatedbiofluids. This layer prevents device degradation and electricalshorting through the surrounding biofluid or to the tissue; its lowmodulus avoids any significant alteration in the overall mechanics, asdescribed above. The frames in FIG. 14A show a few of the μ-ILEDs in thearray deployed subcutaneously, and others on the outer epidermis layerof skin (The white and blue arrows in the images correspond to pixelslocated on the subdermal and epidermal, respectively. The yellow dottedarrows highlight the stitch directions.). Such light emitting,‘photonic’, or ‘light-emitting’, sutures are useful for acceleratedhealing and for transducers of vital signs or physiological parameterssuch as blood oxygenation and perfusion. Alternatively, for longer termimplantable applications, subdermal μ-ILEDs can overcome scatteringlimitations and bring in-vivo illumination to deep layers of tissue.This approach could yield capabilities complementary to those offiber-optic probe-based medical spectroscopic methods, by enablingreal-time evaluation of deep-tissue pathology while allowing precisedelivery of radiation in programmable arrays. Such devices can be formedin geometries of strips or threads, or of sheets. As an example of thelatter, the left frame of FIGS. 14B and S17 show a schematic explodedview and an illustration of fabrication procedures, respectively, for a5×5 array of μ-ILEDs on a thin sheet of polyethylene terephthalate (PET;Grafix DURA-RAR, 50 μm thickness) film coated with an adhesive layer(epoxy) and encapsulated on top and bottom with PDMS. Thin (˜500 μm)ceramic insulated gold wires that connect to metal pads at the peripheryof the array provide access to external power supplies. FIG. 14Cpresents a picture of an animal model with the device implantedsubdermally in direct contact with the underlying musculature (Seemethods section for details). The inset shows the same device beforeimplantation. For continuous operation at the current levels reportedhere, peak increases in temperature at the tissue of a couple of degreesC. are estimated. Short pulsed mode operation could further minimize thepossibility of adverse thermal effects and also, at the same time, allowthe use of phase-sensitive detection techniques for increasinglysophisticated diagnostics, imaging and physiological monitoring.

Use of μ-LED technologies in such applications requires integratedphotonic structures for transmission/collection of light and/or foroptical sensing of surface binding events or changes in local index ofrefraction. In this context, plasmonic crystals represent a useful classof component, particularly for latter purposes. FIG. 15 summarizes anilluminated sensor device that combines thin, molded plasmonic crystalswith arrays of μ-LEDs, in a tape-like format that can be integrateddirectly on flexible tubing suitable for use in intravenous (IV)delivery systems, for monitoring purposes. FIG. 15A provides an explodedview schematic illustration of the system. The plasmonic structureconsists of a uniform layer of Au (50 nm) sputter deposited onto a thinpolymer film embossed with a square array of cylindrical holes (i.e.depressions) using the techniques of soft lithography, as illustrated inFIGS. 15B and 15 c. The relief geometry (depth ˜200 nm; hole diameter˜260 nm; pitch ˜520 nm; see FIG. 15C, and inset of FIG. 15D) andthickness of the Au were optimized to yield measurable changes intransmission associated with surface binding events or variations in thesurrounding index of refraction at the emission wavelength of theμ-LEDs. The full spectral responses appear in FIG. 34. FIG. 15D providestransmittance data measured using a spectrometer over a relevant rangeof wavelengths, for different surrounding fluids (see below fordetails). The completed microsensor devices appear in FIGS. 15E and 15F.As different fluids flow through the tubing, the amount of light thatpasses from the μ-LEDs and through the integrated plasmonic crystalchanges, to provide highly sensitive, quantitative measurements of theindex of refraction. The data of FIG. 15G show the response of arepresentative tube-integrated device, with comparison to calculationsbased on data from corresponding plasmonic structures on rigidsubstrates, immersed in bulk fluids and probed with a conventional,bench-scale spectrometer (FIGS. 34 and 35). This kind of system can beused for continuous monitoring of the dosage of nutrients, such asglucose illustrated here, or of polyethylene glycol (PEG) as illustratedbelow, or other biomaterials of relevance for clinical medicine.

Integration of μ-IPDs with such sensors can yield complete, functionalsystems. To demonstrate this type of capability and also anotherapplication example, a flexible, short range proximity sensor was builtthat could be mounted on machine parts, or robotic manipulators, or foruse in instrumented surgical gloves. This device exploits co-integrationof μ-ILEDs and μ-IPDs in a stretchable format that provides both asource of light and an ability to measure backscatter from a proximalobject. The intensity of this backscatter can be correlated to thedistance to the object. The μ-IPDs use reversed biased GaAs diodes, asfunctional, although inefficient, detectors of light emitted from theμ-ILEDs. A schematic diagram of the integrated system appears in FIG.16A. FIGS. 16B and 16C show this type of system, with 4×6 arrays ofμ-ILEDs and μ-IPDs, integrated onto the fingertip region of a vinylglove. As expected, the photocurrent measured at the μ-IPDs increasesmonotonically with decreasing distance to the object, as shown in theinset of FIG. 16C for different reverse bias voltages (−10, −5, and 0V). FIG. 36A provides I-V characteristics of μ-IPDs. Stacked geometries,such as those presented in FIG. 13D, can also be used, as shown in FIGS.36B-E. Similar to other devices described here, encapsulation with PDMSrenders the systems waterproof. The left and right frames of FIG. 16Dshow images of 4×6 array of μ-ILEDs on a vinyl glove, before and afterimmersion in soapy water. The uniform light emission characteristics ofall devices in the array are clearly apparent. I-V characteristics areinvariant even after operation in saline solution (˜9%) for 3 hours(FIG. 16E) and 1000 cycles of immersion (FIG. 37) in this solution,proving the sustainability of this device inside the body or during usein a surgical procedure.

In summary, the advances described here in mechanics, high fill factormultilayer layouts and biocompatible designs provide important, unusualcapabilities in inorganic optoelectronics, as demonstrated by successfulintegration onto various classes of substrate and by use inrepresentative devices for biomedical and robotics applications.

Methods. Delineating Epitaxial Semiconductor Material for μ-ILEDs andμ-IPDs. For fabrication of the μ-ILEDs and μ-IPDs, the process beganwith epitaxial films that included a quantum well structure(4×(6-nm-thick Al_(0.25)Ga_(0.25)In_(0.5)P barriers/6-nm-thickIn_(0.56)Gao.44P wells)/6-nm-thick Al_(0.25)Ga_(0.25)In_(0.5)P barriers)and an underlying sacrificial layer of Al_(0.96)G_(0.04)As on a GaAswafer. Details appear in FIG. 17A. Inductively coupled plasma reactiveion etching (ICP-RIE; Unaxis SLR 770 system) with Cl₂/H₂ through a hardmask of SiO₂ formed trenches down to the Al_(0.96)G_(0.04)As, todelineate active materials in 6×6 or 8×8 or 3×8 or 1×4 arrays of squareswith sizes of 100 μm×100 μm. Next, photolithography defined photoresiststructures at the four corners of each square to hold the epitaxiallayers to the underlying GaAs wafer during removal of theAl_(0.96)G_(0.04)As with diluted hydrofluoric (HF, Transene, USA) acid(deionized water (DI): 49% HF acid=1:100).

Fabricating Arrays of μ-ILEDs and μ-IPDs in Mesh Designs with SerpentineInterconnects on Glass Substrates. The released squares of epitaxialmaterial formed according to procedures described above were transferprinted onto a glass substrate coated with layers of a photodefinableepoxy (SU8-2; Microchem.; 1.2 μm thick), polyimide (PI; Sigma-Aldrich;1.2 μm thick), and poly(methylmethacrylate) (PMMA A2; Microchem.; 100 nmthick) from top to bottom. Next, another layer of epoxy (SU8-2, 2.0 μm)was spin-cast and then removed everywhere except from the sidewalls ofthe squares by reactive ion etching (RIE; PlasmaTherm 790 Series) toreduce the possibility of partial removal of the bottom n-GaAs layerduring the 1st step of an etching process (1st step:H₃PO₄:H₂O₂:DI=1:13:12 for 25 seconds/2nd step: HCl:DI=2:1 for 15seconds/3rd step: H₃PO₄:H₂O₂:DI=1:13:12 for 24 seconds) that exposed thebottom n-GaAs layer for n-contacts. Next, another layer of epoxy (1.2 μmthick) spin-cast and photopatterned to expose only certain regions ofthe top p-GaAs and bottom n-GaAs, provided access for metal contacts(non-Ohmic contacts) and interconnect lines (Cr/Au, 30 nm/300 nm)deposited by electron beam evaporation and patterned by photolithographyand etching. These lines connected devices in a given row in series, andadjacent rows in parallel. A final layer of spin cast epoxy (2.5 μm)placed the devices and metal interconnects near the neutral mechanicalplane. Next, the underlying polymer layers (epoxy/PI/PMMA) were removedin regions not protected by a masking layer of SiO₂ (150 nm thick) byRIE (oxygen plasma, 20 sccm, 150 mtorr, 150 W, 40 min). Wet etching theremaining SiO₂ with buffered oxide etchant exposed the metal pads forelectrical probing, thereby completing the processing of arrays ofμ-ILEDs (and/or μ-IPDs) with serpentine interconnects.

Transfer Printing of Stretchable Arrays of Devices to Substrates ofInterest. Dissolving the PMMA layer of the structure described abovewith acetone at 75° C. for 10 minutes released the interconnected arrayof devices from the glass substrate. Lifting the array onto a flatelastomeric stamp and then evaporating layers of Cr/SiO₂ (3 nm/30 nm)selectively onto the backsides of the devices enabled strong adhesion tosheets or strips of PDMS or to other substrates coated with PDMS. Forthe PDMS balloon of FIG. 11D, prestrain was applied by partiallyinflating the balloon, followed by transfer printing the μ-ILEDs andthen releasing (deflating) the balloon. For small substrates, rollerprinting techniques were used. See below for details.

Stretching Tests and Electrical Characterization. Stretching tests wereperformed using custom assemblies of manually controlled mechanicalstages, capable of applying strains along x, y, and diagonal directions.For fatigue testing, one cycle corresponds to deformation to a certainlevel and then return to the undeformed state. Each fatigue test wasperformed up to 1000 cycles to levels of strains similar to those shownin the various figures. Electrical measurements were conducted using aprobe station (4155C; Agilent), by directly contacting metal pads whilestretched, bent, or twisted. For FIG. 12D, the measurement was performedusing a lead-out conductor line, bonded to metal pads of the arrays ofμ-ILEDs. Typical voltage scan ranges for measurement of the 6×6, 8×8,and 3×8 arrays was 0˜60 V, 0˜80V, and 0˜90V, respectively.

Animal Experiments. All procedures were performed under approved animalprotocols. A female Balb/c mouse was anesthetized with anintraperitoneal injection of a mix of ketamine/xylazine. The depth ofanesthesia was monitored by palpebral and withdrawal reflexes to confirmthat the animal had reached “stage 3” of anesthesia. Once the animal waslightly anesthetized, the back was shaved and cleaned at the incisionsite with 70% ethanol, followed by a betadine surgical scrub. Previousimplants were removed from the mouse and the animal was euthanizedaccording to approved protocols. To validate the performance of suturesin real conditions, the incision opened during surgery was closed with acustomized 16-gauge needle and three passes with the light emittingsuture were performed to seal the wound. The suture was then tested byverifying the proper operation of the μ-ILEDs. For the implants, theincision was performed on the dorsal side of the mouse and the suturingwas carried out across the dermal layers (outer layers and subcutaneoustissues) above the muscle tissue.

Fabrication of Thin Plasmonic Crystals on Plastic. Soft lithographytechniques were used to form structures of surface relief on thin layersof a photocurable polyurethane (PU, NOA 73, Norland Products) cast ontosheets of poly(ethylene terephthalate). Sputter deposition (5 mTorr Arenvironment; AJA sputtering system) of uniform, thin (˜50 nm) layers ofgold completed the fabrication. The geometry of the relief and thethickness of the gold were selected to optimize the performance of theplasmonic crystals at the emission wavelength of the μ-ILEDs.

Spectroscopic Measurement of Transmission Properties of the PlasmonicCrystals. Transmission spectra were measured using a Varian 5GUV-Vis-NIR spectrophotometer operating in normal incidence transmissionmode, without temperature control. A flow cell was mounted on top of theplasmonic crystal and aqueous solutions of glucose with differentconcentrations/refractive indexes were injected with a syringe pump(Harvard Apparatus) at a flow rate of 0.2 mL/min. Transmission spectraover a wavelength range of 355-1400 nm were collected during the processto monitor changes in multiple plasmonic responses. Such data were usedin the process of optimizing the layouts of the crystals, and forinterpreting measurements collected with the flexible, illuminated andtube-integrated sensors.

Fabrication and Testing of Flexible, Illuminated Plasmonic CrystalSensors. The procedure for integrating a plasmonic crystal with μ-ILEDlight sources on a tube (Tygon R-3603, inner and outer diameter: 0.318mm and 0.476 mm, respectively), began with formation of a contact windowby cutting an opening in the tube, to enable direct contact of fluid inthe tube with the plasmonic crystal. The embossed side of the crystalwas placed face down against the window and then sealed with atransparent adhesive tape. Next, a thin layer of PDMS was coated on thetape and adjacent regions of the tubing as a bonding layer for atransfer printed, stretchable array of μ-ILEDs aligned to the plasmoniccrystal. This step completed the integration process. Light from thedevice was collected with a separate, commercial Si photodetector(ThorLabs, Model DET110) placed on the opposite side of the tubing.Output from the detector was sampled digitally at a rate of 10 kHz.Averaging times of 6 seconds were used for each recorded data point.

Photographs. Images in FIGS. 11A and 13E were combined images toeliminate out-focused regions. Tens of pictures were captured atdifferent focal depths using a Canon 1Ds Mark III with a Canon MP-E 1-5xMacro lens, and those captured pictures are merged in the software“helicon focus” to create completely focused image from severalpartially focused images.

Figure Captions. FIG. 11. Device layouts of μ-ILED arrays and theirresponses to uniaxial and balloon-shape biaxial stretching. FIG. 11A,Optical image of a 6×6 array of μ-ILEDs (100 μm×100 μm, and 2.5 μmthick, in an interconnected array with a pitch of ˜830 μm) withnon-coplanar serpentine bridges on a thin (˜400 μm) PDMS substrate (leftframe). Schematic illustration (right) and corresponding photograph(inset) of a representative device, with encapsulation. FIG. 11B,Optical images of a stretchable 6×6 array of μ-ILEDs, showing uniformemission characteristics under different uniaxial applied strains (topleft: 0%, bottom left: 48% along horizontal direction, top right: 0%,bottom right: 46% along diagonal direction). FIG. 11C, Current-voltage(I-V) characteristics of this array measured in the strainedconfigurations shown in b (left) and voltage at 20 μA current fordifferent cycles of stretching to 75% along the horizontal direction(right). FIG. 11D, Tilted (left) view optical images of a stretchablearray (6×6) of μ-ILEDs on a thin (˜500 μm) PDMS membrane in a flatconfiguration (top) and in a hemispherical, balloon state (bottom)induced by pneumatic pressure. FIG. 11E, the magnified view of FIG. 11Dfrom the top. The yellow dashed boxes highlight the dimensional changesassociated with the biaxial strain. FIG. 11F, I-V characteristics of thearray in its flat and inflated state. FIG. 11G, Distribution ofmeridional and circumferential strains determined by 3D-FEM.

FIG. 12. Responses of μ-ILED arrays to twisting and stretching on sharptips. FIG. 12A, Optical images of an array of μ-ILEDs (3×8) on a band ofPDMS twisted to different angles (0° (flat), 360°, and 720° from top tobottom), collected with (left) and without (right) externalillumination. FIG. 12B, SEM image of the array when twisted to 360°. Theserpentine interconnects move out of the plane (red box) to accommodatethe induced strains. FIG. 12 , I-V characteristics of the array twistedby various amounts (0 (flat), 360 and)720°. FIG. 12C, Distributions ofaxial (left), width (center) and shear (right) strain determined by3D-FEM for twisting to 720°. FIG. 12E, Optical images of an array ofμ-ILEDs (6×6), tightly stretched on the sharp tip of a pencil, collectedwith (left) and without (right) external illumination. The white arrowsindicate the direction of stretching. FIG. 12F, Optical images of astretchable 8×8 array wrapped and stretched downward on the head of acotton swab. The inset image was obtained without external illumination.FIG. 12G, I-V characteristics of the array in FIG. 12E, before(initial), during (deformed) and after (released) deformation. The insetprovides a graph of the voltage needed to generate a current of 20 μA,measured after different numbers of cycles of deformation.

FIG. 13. Multilayer laminated configurations of arrays of μ-ILEDs forhigh effective area coverage and integration on various unusualsubstrates. FIG. 13A, Schematic, exploded view illustration for astacked device formed by multilayer lamination. FIG. 13B, Optical imagesof a four layer stack of 4×4 arrays with layer-to-layer offsets designedto minimize overlap of interconnect lines with positions of the μ-ILEDs.The images show emission with different numbers of layers in operation(1st layer on, 1st and 2nd layers on, 1st, 2nd and 3rd layers on, and1st, 2nd, 3rd and 4th layers on). FIG. 13C, Optical images of a twolayer stack of 8×8 arrays, with different layers in operation. The insetshows the device in a bent state (bending radius ˜2 mm) with both layerson. FIG. 13D, Optical image of an array of μ-ILEDs (8×8) on a piece ofpaper, in a folded state (bending radius ˜400 μm) during operation. Theinset shows the device in its flat state. FIG. 13E, Image of a 6×6 arrayon a sheet of aluminum foil under crumpled state. The inset shows thedevice in its flat state. FIG. 13F, Images of a 6×6 array on a catheterballoon in its inflated (inset) and deflated states. FIG. 13G, Images ofa thin (˜8 μm), narrow (820 μm) strip of μ-ILEDs (1×8) with serpentineinterconnects on a rigid plastic tube (diameter ˜2.0 mm, left). Insetshows the magnified view of a single pixel. FIG. 13H, a thin strip LEDdevice consisting of an isolated μ-ILED with straight interconnectswrapped around a glass tube (diameter ˜5.0 mm, right). The insetsprovide a magnified view. FIG. 13I, Image of a 1×8 array with serpentinemetal bridges on a ˜700 μm diameter fiber, wrapped around a glass tube(diameter ˜1.4 mm, left frame) and, in a knotted state (inset),respectively, resting on coins (pennies) to set the scale.

FIG. 14. Demonstrations of application possibilities for systems ofμ-ILEDs in biomedicine. FIG. 14A, Light emitting suture consisting of a1×4 array of μ-ILEDs on a thread (diameter ˜700 μm), demonstrated in ananimal model with a conventional suture needle. The images correspond toone stitch in its off state, after one stitch, two stitches, and threestitches in the on state, in the clockwise direction from the top leftframe, respectively. The yellow arrows indicate the suturing directions.FIG. 14B, Schematic exploded view illustration of an array of μ-ILEDs(5×5) on a thin PET film (50 μm thick) coated with an adhesive. Layersof PDMS on the top and bottom provide a soft, elastomeric encapsulationthat offers biocompatibility and an excellent barrier to biofluids andsurrounding tissue. FIG. 14C, Image of an animal model with this arrayimplanted under the skin, and on top of the muscle tissue. The insetshows the device before implantation.

FIG. 15. Refractive index microsensors based on thin, molded plasmoniccrystals integrated with arrays of μ-LEDs, in tape-like formatsintegrated directly on flexible tubing suitable for use in intravenous(IV) delivery systems. FIG. 15A, Schematic exploded view of thesensor/tube system. FIG. 15B, Thin, molded plasmonic crystal on aplastic substrate wrapped around a cylindrical support, showing colorsdue to diffraction. FIG. 15C, Atomic force microscope image of thesurface of such a crystal. FIG. 15D, Normal incidence transmissionspectra collected with a commercial spectrometer over a range ofwavelengths relevant for illumination with red μ-LEDs. FIG. 15E, Imageof a sensor integrated on an flexible plastic tube (Tygon), next to thetip of a pen. The inset shows the backside of the plasmonic crystalbefore integration of the μ-ILEDs. FIG. 15F, Images of thetube-integrated sensor viewed from the μ-ILED side of the device, withdifferent fluids in the tube. FIG. 15G, Measurement results from arepresentative sensor (top), operated while integrated with a tube, as asequence of aqueous solutions of glucose pass through. The bottom frameshows the percentage increase in light transmitted from the μ-ILED,through the plasmonic crystal and measured on the opposite side of thetube with a silicon photodiode, as a function of glucose concentration.The calculations are based on the response of a separate, conventionalplasmonic crystal evaluated using bulk solutions and a commercialspectrometer.

FIG. 16. Stretchable optical proximity sensor based on an array ofμ-ILEDs and μ-IPDs mounted on the fingertip of a vinyl glove. FIG. 16A,Schematic illustration of co-integrated 2×6 arrays of μ-ILEDs and μ-IPDsto yield a thin, stretchable optical proximity sensor. FIG. 16B, Imageof the sensor, mounted on the fingertip region of a vinyl glove. FIG.16C, Optical images of an array of μ-ILEDs (4×6) with serpentine metalbridges, transfer-printed on the fingertip region of a vinyl glove. Theinset shows a plot of photocurrent as a function of distance between thesensor and an object (white filter paper) for different reverse bias anddifferent voltages. FIG. 16C, Left and right frames correspond to imagesbefore and after immersion into soapy water. FIG. 16D, IVcharacteristics of the same μ-ILEDs array as shown in FIG. 16C afteroperation in saline solution (˜9%) for different immersion time.

Contact Scheme. Here, simple metal (Cr/Au) to doped GaAs contacts areused instead of ohmic contacts. For improved electrical characteristics,conventional ohmic contacts of metal interconnects to GaAs can beimplemented. To form the ohmic contact, a series of metal stacksfollowed by appropriate annealing (n ohmic contact metals: Pd/Ge/Aufollowed by anneal at 175° C. for 1 hour, p ohmic contact metal:Pt/Ti/Pt/Au in this paper) can be used, which results in lower take-offvoltage can be obtained as shown in FIG. 38A.

Long-term operation. Long-term operation was tested using two LEDdevices, connected in series, on a thin slab of PDMS was performed underthe constant current mode (0.75 mA). Both devices showed robust andreliable performance during the continuous operation for 100 hourswithout affecting I-V characteristics as shown in FIG. 38B.

FEM Simulation of Balloon Deformation. FIG. 39A illustrates themechanics model for inflating and transfer printing onto the PDMSballoon of FIG. 11. The initially flat, circular thin film (initialstate, upper left frame of FIG. 24A) of radius r is fixed at its outerboundary, and is inflated by air to a spherical cap of height h(inflated state, right frame of FIG. 39A). The radius of the sphere isR=(h²+r²)/(2h). The spherical cap is pressed down and flattened duringtransfer printing, as shown in the lower left frame of FIG. 39A(as-print state). The deformation is uniform along the meridionaldirection during inflation, while all material points move verticallydownward during printing. Therefore, for a point of distance xo to thefilm center at the initial state, its position changes to xi in theinflated state with an arc distance s₁ to the film center, and thenchanges to x₂ in the state during printing, where s₁=(R_(x0)/r)arcsin(r/R) and x₁=x₂=R sin[(x₀/r)sin⁻¹(r/R)]. These give the meridionaland circumferential strains of the inflated state as:

$\begin{matrix}{{ɛ_{\theta 1} = {{\frac{R}{r}\arcsin\frac{r}{R}} - 1}},} & ({S1}) \\{ɛ_{\varphi 1} = {{\frac{R}{x_{0}}{\sin\left( {\frac{x_{0}}{r}\arcsin\frac{r}{R}} \right)}} - 1.}} & \left( {S\; 2} \right)\end{matrix}$The meridional and circumferential strains at the state during printingare given by:

$\begin{matrix}{{ɛ_{\theta 2} = {{\frac{R}{r}{\cos\left( {\frac{x_{0}}{r}\sin^{- 1}\frac{r}{R}} \right)}\sin^{- 1}\frac{r}{R}} - 1}},} & ({S3}) \\{ɛ_{\varphi 2} = {{\frac{R}{x_{0}}{\sin\left( {\frac{x_{0}}{r}\sin^{- 1}\frac{r}{R}} \right)}} - 1}} & \left( {S\; 4} \right)\end{matrix}$Finite element method (FEM) was used to study this process in order tovalidate the analytical model above. The contours of meridional andcircumferential strains of the inflated state appear in the upper andlower left frames of FIG. 39B, respectively. The results are comparedwith analytical solutions, Equations (S1) and (S2), in the right frameof FIG. 39B, and show good agreement. Therefore, the analyticalformulae, Equations (S1) and (S2), can be used to predict the PDMSstrain under different inflation, and further to estimate the strain indevices on the balloon surface. FIG. 39C shows the contours ofmeridional (upper left frame) and circumferential (lower left frame)strains of the asprint state, and the comparison with analyticalsolutions from Equations (S3) and (S4) (right frame). The analyticalsolutions, once again, agree well with FEM simulations without anyparameter fitting.

Bending of LEDs on Various Substrates. The LED, as illustrated in FIG.40, consists of multiple layers with thicknesses h₁=3.5 μm, h₂=2.5 μm,h₃=1.2 μm and h₄=1.2 μm, and Young's moduli are E_(SU8)=5.6 GPa,E_(GaAs)=85.5 GPa and E_(PI)=3.2 GPa. These layers are modeled as acomposite beam with equivalent tensile and bending stiffnesses. The PDMSstrain isolation layer has thickness h₅=50 um and Young's modulusE_(PDMS)=0.4 MPa. The Young's modulus E_(sub) and thickness H of thesubstrate are 1.2 MPa and 0.8 mm for the fabric, 23.5 MPa and 0.5 mm forthe fallen leaf, and 600 MPa and 0.2 mm for the paper. The strainisolation model then gives very small maximum strains in GaAs, 0.043%,0.082% and 0.23% for the completely folded fabric, leaf and paper,respectively. The minimal bend radii are the same as the correspondingsubstrate thicknesses H, i.e., 800 μm, 500 μm and 200 μm for the fabric,leaf and paper, respectively. For the Al foil substrate, the minimumbend radius is obtained as 139 μm when the strain in GaAs reaches 1%.

Without the PDMS strain isolation layer, the LED and substrate aremodeled as a composite beam. The position of neutral axis (measured fromthe top surface) is given by:

$y_{0} = {\frac{\begin{Bmatrix}{{E_{SUS}\left\lbrack {\left( {h_{1} + h_{3}} \right)^{2} + {2h_{2}h_{3}}} \right\rbrack} + {E_{PI}{h_{4}\left( {{2h_{1}} + {2h_{2}} + {2h_{3}} + h_{4}} \right)}}} \\{{{+ E_{GaAs}}{h_{2}\left( {{2h_{1}} + h_{2}} \right)}} + {E_{sub}{H\left( {{2h_{1}} + {2h_{2}} + {2h_{3}} + {2h_{4}} + H} \right)}}}\end{Bmatrix}}{2\left\lbrack {{E_{{SU}\; 8}\left( {h_{1} + h_{3}} \right)} + {E_{GaAs}h_{2}} + {E_{PI}h_{4}} + {E_{sub}H}} \right\rbrack}.}$The maximum strain in GaAs is

${ɛ_{GaAs} = {\frac{1}{R_{b}}{\max\left( {\left| {y_{0} - h_{1}} \right|,\left| {h_{1} + h_{2} - y_{0}} \right|} \right)}}},$where R_(b) is the bending radius. Therefore, the minimum bending radiusof LED array on the substrate is

${R_{b} = {\frac{1}{ɛ_{failure}}{\min\left( {\left| {y_{0} - h_{1}} \right|,\left| {h_{1} + h_{2} - y_{0}} \right|} \right)}}},$where ε_(failure)=1% is the failure strain of GaAs. For the fabricsubstrate, the maximum strain in GaAs is only 0.34% even when it iscompletely folded, which gives the minimum bending radius the same asthe thickness 0.8 mm. For the fallen leaf and the paper, the minimumbending radii are 1.3 mm and 3.5 mm.

Figure Captions. FIG. 17. Schematic illustration of epitaxial layer (a)and fabrication processes for μ-ILEDs arrays on a carrier glasssubstrate after transfer printing (b).

FIG. 18. (18A) Schematic illustration (left frame) and correspondingmicroscope (top right frame) and SEM (bottom right frame) images of a6×6 μ-ILEDs on a handle glass substrate coated with layers of polymers(epoxy/PI/PMMA). (18B) Schematic illustration (left frame) andcorresponding microscope (top right frame) and optical (bottom rightframe) images of a 6×6 μ-ILEDs array which is picked up with a PDMSstamp for transfer printing. A shadow mask for selective deposition ofCr/SiO₂ (thickness: 3 nm/30 nm) covers the retrieved array on a softelastomeric PDMS stamp. (18C) Schematic illustration of transferprinting to a pre-strained thin (thickness: ˜400 μm) PDMS substrate(left frame) and microscope (top right frame) and SEM (bottom rightframe) images of the transferred μ-ILEDs array on a prestrained thinPDMS substrate. Prestrain value was ˜20%.

FIG. 19. (19A) Schematic illustration of top encapsulation layersindicating some of the key dimensions. (19B) Schematic illustration ofthe cross sectional structure at an island, with approximate thicknessesfor each layer. The inset corresponds to an SEM image of a μ-ILEDs arrayafter transfer printing to a thin PDMS substrate with prestrain of ˜20%.(19C) Schematic illustration of the cross sectional structure at metalinterconnection bridges, with approximate thicknesses of each layer.

FIG. 20. (20A) Tilted view SEM images of adjacent μ-ILEDs (yellow dashedboxes) before (left, formed with ˜20% pre-strain) and after (right)stretching along the horizontal direction (red arrows). (20B) Straindistributions determined by 3D-FEM for the cases corresponding to framesin (20A). The black outlines indicate the positions of the devices andthe serpentines before relaxing the pre-strain.

FIG. 21. (21A) Optical microscope images of two pixels in a μ-ILEDsarray with a serpentine bridge design before (left frame) and after(right frame) external stretching along the horizontal direction. Theupper and lower images show optical micrographs in emission light off(upper) and on (lower) states. The distance between adjacent pixelsappears in the lower images and used for calculation of applied strains.The lower images were obtained without external illumination. (21B)Optical micrograph images of two pixels in a μ-ILEDs array before (leftframe) and after (right frame) external stretching along the diagonaldirection. (21C) FEM simulation under external stretching along thediagonal direction (left frame), and strain contours in the GaAs activeisland (top right frame) and the metal bridge (bottom right frame).

FIG. 22. Optical images of a 6×6 μ-ILEDs array with a serpentine meshdesign with external illumination under the same strain circumstances asFIG. 11B.

FIG. 23. (23A) Optical image of an 8×8 μ-ILEDs array on a thin PDMSsubstrate in its on state, which is under the same kind of deformedcondition as bottom left frame of FIG. 11d . (23B) Top view opticalimages of same array as FIG. 11D in its ‘flat’ (left frame) and‘inflated’ state (right frame) without external illumination. (23C)Spatial distribution of FEM results of the right frame of FIG. 11D andanalytical solutions calculated from Equations (S1) and (S2).

FIG. 24. (24A) Schematic illustrations of a 3×8 μ-ILEDs array integratedon a thin PDMS substrate with detailed dimensions (upper frame:registrations of the μ-ILEDs on a PDMS donor substrate, lower frame:entire view of the printed 3×8 μ-ILEDs array). The inset on toprepresents an optical microscope image of this μ-ILEDs array on a handleglass substrate before transfer printing. (24B) Magnified view of theSEM image in FIG. 12B. The white dotted rectangle highlights thenon-coplanar bridge structures. (24C) Voltage at 20 μA current for eachtwisting cycle of 360°.

FIG. 25. FEM strain contours of axial (top), width (center), and shear(bottom) strains for 360° twisted PDMS substrate.

FIG. 26. Fatigue test result of a 6×6 μ-ILEDs array as shown in FIG.12E. (26A) Plot of I-V characteristics of a 6×6 μ-ILEDs array as afunction of deformation cycles. (26B) Plot of voltage needed to generatea current of 20 μA measured after deformation cycles up to 1000 times.Each deformed state is approximately same as shown in FIG. 12E.

FIG. 27. (27A) Schematic illustration of stacked devices describingstates of FIG. 13B. (27B) Optical images of stacked devices as shown inFIG. 13B, collected without external illumination.

FIG. 28. (28A) The strain distribution of the two-layer system in thestacked array bent to a radius of curvature 2 mm, as shown in FIG. 13C.The black dashed rectangles demonstrate the positions of μ-ILEDs. (28B)The strain distribution in GaAs layers in the μ-ILEDs island.

FIG. 29. (29A) Optical image of a 6×6 μ-ILEDs array with serpentinemetal interconnects, integrated on fabrics, in its bent and on state(bending radius ˜4.0 mm). The inset shows the device in its flat and offstate. (29B) Plot of I-V characteristics of this array in its bentstate. Inset provides a graph of the voltage needed to generate acurrent of 20 μA, measured after different numbers of cycles of bendingdeformation. (29C) Optical image of an 8×8 μ-ILEDs array with a humanpattern, integrated on a fallen leaf, in its bent and on state. Theinset image was collected with external illumination. (29D) Plot of I-Vcharacteristics in the bent state as shown in FIG. 29C. (29E) Opticalimage of a μ-ILEDs array integrated on a paper in its folded and onstate. (29F) Optical image of the same μ-ILEDs array as shown in FIG.13E in its mildly crumbled state. Inset represents microscope image ofadjacent four pixels in their on states.

FIG. 30. (30A) Plot of I-V characteristics of a 6×6 μ-ILEDs arrayintegrated on paper in its flat (FIG. 13D inset) and folded (FIG. 13D)state. (30B) Plot of I-V characteristics of a 6×6 μ-ILEDs arrayintegrated on aluminum foil in its flat (FIG. 13E inset) and crumbled(the center frame of FIG. 13E) state. (30C) Fatigue tests of arrays of6×6 μ-ILEDs as shown in FIG. 29E. Plot of I-V characteristics of aμ-ILEDs array integrated on paper as a function of deformation cycles(left frame). Plot of voltage needed to generate a current of 20 μAmeasured after deformation cycles up to 1000 times (right frame). (30D)Fatigue tests of arrays of 6×6 μ-ILEDs as shown in FIG. 29F. Plot of I-Vcharacteristics of a μ-ILEDs array integrated on aluminum foil as afunction of deformation cycles (left frame). Plot of voltage needed togenerate a current of 20 μA measured after deformation cycles up to 1000times (right frame).

FIG. 31. SEM images of various substrate such as fabrics (31A), Al foils(31B), paper (31C), and fallen leaves (31D) before (left frame) andafter (right frame) coating of thin layer of PDMS.

FIG. 32. Optical image of single μ-ILED with long straightinterconnects, integrated on a flexible thread with diameter of diameter˜2.5 mm (32A), and diameter ˜0.7 mm (32B), respectively. (32C) Opticalimage of a single LED device with long interconnects, integrated on ˜300μm-wide threads in its bent and un-deformed (inset) states,respectively. (32D) Schematic illustration describing ‘rolling method’.(32E) Optical image of a 4×6 μ-ILEDs array with serpentine bridgeinterconnects integrated on a glass tube using a rolling method forprinting. (32F) The suture demonstration using μ-ILEDs array mounted ona thread for radiation therapy with an incision in paper (threaddiameter ˜700 μm).

FIG. 33. Schematic illustration of the encapsulation of an implantablearray of μ-ILEDs as described in FIGS. 14B and 14C.

FIG. 34. (34A) Light intensity spectrum of single μ-ILED, measured withconventional spectrometer (Ocean Optics, USA). (34B) Percenttransmittance spectrum through plasmonic nanohole array, measured withconventional spectrometer (CARY, Varian, USA). (34C) Transmitted lightintensity spectrum through plasmonic nanohole array at the relevantwavelength range, calculated by multiplying single LED intensity in(34A) and % transmittance in (34B).

FIG. 35. (35A) Measurement results from a representative sensor (top),operated while integrated with a tube, as a sequence of aqueoussolutions of PEG (polyethylene glycol) pass through. (35B) Thepercentage increase in light transmitted from the μ-ILED, through theplasmonic crystal and measured on the opposite side of the tube with asilicon photodiode, as a function of PEG concentration. (35C) Refractiveindexes change with different glucose and PEG concentrations.

FIG. 36. (36A) Plot of I-V characteristics of photodiodes at differentdistances between an optical proximity sensor and an approaching objectas explained in FIGS. 16A-C. (36B) Plot of I-V characteristics of 2ndlayer (an array of photodiode) as a function of the current level of 1stlayer (an array of μ-ILEDs) under negative bias in the stacked device.(36C) Plot of photocurrent of an array of 6×6 p-PDs that is stacked onthe layer of a 6×6 μ-ILEDs array as a function of operation current ofμ-ILEDs in the stacked device. (36D) Plot of current-voltagecharacteristics of an array of 6×6 photodiodes as a function of distancebetween the device and the approaching object in the stacked device.Voltage range of an array of 6×6 μ-PDs was from 0 V to −10 V during the6×6 μ-ILEDs array was in emission light up state (operation current ofμ-ILEDs array: 3 mA). (36E) Re-plotting of FIG. 36D as a function ofdistance between approaching object and μ-PDs.

FIG. 37. IV characteristics of the same μ-ILEDs array as shown in FIG.16C at different immersion times.

FIG. 38. (38A) Result of Luminance (L)—Current (I)—Voltage (V)measurement of an individual pixel with and without applied ohmiccontacts. (38B) Applied voltage to generate a current of 20 μA, measuredafter different operation time. The inset provides I-V characteristicswith different operation time.

FIG. 39. (39A) Schematic illustration of analytical model for theinflation and printing-down of PDMS film. (39B) FEM contours ofmeridional (upper left) and circumferential (lower left) strains of theinflated state and its comparison with analytical solutions calculatedfrom Equations (51) and (S2). (39C) FEM contours of meridional (upperleft) and circumferential (lower left) strains of the as-printed stateand its comparison with analytical solutions Equations (S3) and (S4)(right frame).

FIG. 40. Schematic illustration of the cross section of μ-ILEDs on asubstrate.

EXAMPLE 2 Smart Sutures

FIG. 41A provides typical designs smart suture thread embodiments. Thin(˜1 mm) and long (˜30 mm) threads that include a silicon diode basedtemperature sensor or a platinum resistor based temperature sensor canbe fabricated on a rigid handle substrate, such as a wafer or glasssubstrate. The top image shows a smart suture design including fourindividually addressable silicon diode temperature sensors. The bottomimage shows a smart suture including two individually addressableplatinum resistor temperature sensors and two individually addressableresistive heating elements. Each of these smart sutures thread designsfeature a 6 mm inter-element spacing and electrical interconnections toan external controller.

FIG. 41B shows optical images of two smart suture thread embodimentswith expanded view images of silicon diode (top) and platinum resistor(bottom right) temperature sensors. Additional functions can also beadded beyond temperature sensing. For example, a gold microheater thatuses resistive Joule heating can be integrated together for localheating, as shown in the expanded view image (bottom left). Localheating, together with appropriate polymers containing pharmaceuticalcompositions, can be utilized to selectively release the pharmaceuticalcompositions controllably at a desired time and location.

FIG. 41E shows typical current-voltage (IV) curves at differenttemperatures. The voltages at fixed current, for example at 10 μA, canbe plotted versus temperature, as shown in FIG. 41D, which shows alinear calibration curve for the temperature sensing. Platinum resistorsexhibit different resistance values at different temperatures, asplotted in FIG. 41C. When combined or used separately, these temperaturesensors integrated on smart suture threads and sutured around targettissues, can monitor the local temperature to detect abnormaltemperature increases, for example as caused by a local inflammation.

FIG. 41F shows an optical image the resulting smart suture threadincluding a silicon diode temperature sensor on one side of the sutureand a gold heating element on the other side of the suture.

Intentionally offset temperature sensors, as shown in the two sidedsmart suture thread design shown in FIG. 41G, provides spatiallyincreased detection ability versus a smart suture thread havingtemperature sensors aligned on opposite sides of the smart suturethread.

EXAMPLE 3 Effect of Bending on Fluid Monitors

FIG. 42A shows a schematic diagram of a fluid monitor embodiment, shownhere as a refractive index micro-sensor which has a thin, moldedplasmonic crystal integrated with μ-LEDs on a flexible tube in flat andbent states. In the device shown, the μ-LED array has fixed dimensionsof 100 μm×100 μm; the bending radius of the tube as is limited to besmaller than 4× the tube diameter to avoid folding. Additionally, theμ-LEDs and the μ-PDs are in conformal contact on a tube under any bentcondition. A simple geometric calculation of collection apertures andoutermost light path length based on the illustration shown FIG. 42Aestablishes the effects of bending on μ-PDs size and separation distancebetween the μ-LEDs and the μ-PDs (i.e. the outer diameter of the tube)on sensitivity. Here, sensitivity is defined as the difference of lightamount that the μ-PDs can collect in flat and bent states.

FIG. 42B shows an enlarged view. The geometric calculation by lighttracing reveals that the sensitivity with bending deformation isaffected by μ-PDs size and tube diameter but, it change in sensitivityis negligible (<0.5%), partly due to the very small μ-LED array size andinvariant solid angle of light from μ-LEDs to μ-PDs. The sensitivity dueto bending can be further decreased by use of a small μ-PD array.

For the configuration shown in FIG. 41A, the effective μ-PD array areadecreases by 0.22% with an increase in the outermost path of light of0.2%. For a configuration with a tube of 2.5 mm, a μ-PD array of 1×1 mm,a μ-LED array of 100×100 μm, an outer radius of curvature of 20 mm andinner radius of curvature of 17.5 mm, the effective μ-PD array areadecreases by 0.12% with an increase in the outermost path of light of0.2%. For a configuration with a tube of 2.5 mm, a μ-PD array of 500×500μm, an LED array of 100×100 μm and an outer radius of curvature of 20 mmand inner radius of curvature of 17.5 mm, the effective μ-PD array areadecreases by 0.04% with an increase in the outermost path of light of0.15%. These latter results demonstrate that the sensitivity to bendingdeformation is dependent upon the μ-PD array size when all other factorsremain constant.

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STATEMENTS REGARDING INCORPORATION BY REFERENCE AND VARIATIONS

All references throughout this application, for example patent documentsincluding issued or granted patents or equivalents; patent applicationpublications; and non-patent literature documents or other sourcematerial; are hereby incorporated by reference herein in theirentireties, as though individually incorporated by reference, to theextent each reference is at least partially not inconsistent with thedisclosure in this application (for example, a reference that ispartially inconsistent is incorporated by reference except for thepartially inconsistent portion of the reference).

The following references relate generally to flexible and/or stretchablesemiconductor materials and devices and are each hereby incorporated byreference in its entirety: U.S. patent application Ser. No. 12/778,588,filed on May 12, 2010, PCT International Application No. PCT/US05/19354,filed Jun. 2, 2005 and published under No. WO2005/122285 on Dec. 22,2005, U.S. Provisional Patent Application No. 61/313,397, filed Mar. 12,2010, U.S. patent application Ser. No. 11/851,182, filed Sep. 6, 2007and published under No. 2008/0157235 on Jul. 3, 2008, and PCTInternational Application No. PCT/US07/77759, filed Sep. 6, 2007 andpublished under No. WO2008/030960 on Mar. 13, 2008.

The following references relate generally to bioresorbable substratesand methods of making bioresorbable substrates and are each herebyincorporated by reference in its entirety: PCT Patent ApplicationPCT/US03/19968 filed Jun. 24, 2003, PCT Patent ApplicationPCT/US04/000255 filed 1/7/2004, PCT Patent Application PCT/US04/11199filed Apr. 12, 2004, PCT Patent Application PCT/US05/20844 filed Jun.13, 2005, and PCT Patent Application PCT/US06/029826 filed Jul. 28,2006.

All patents and publications mentioned in the specification areindicative of the levels of skill of those skilled in the art to whichthe invention pertains. References cited herein are incorporated byreference herein in their entirety to indicate the state of the art, insome cases as of their filing date, and it is intended that thisinformation can be employed herein, if needed, to exclude (for example,to disclaim) specific embodiments that are in the prior art. Forexample, when a compound is claimed, it should be understood thatcompounds known in the prior art, including certain compounds disclosedin the references disclosed herein (particularly in referenced patentdocuments), are not intended to be included in the claim.

When a group of substituents is disclosed herein, it is understood thatall individual members of those groups and all subgroups and classesthat can be formed using the substituents are disclosed separately. Whena Markush group or other grouping is used herein, all individual membersof the group and all combinations and subcombinations possible of thegroup are intended to be individually included in the disclosure. Asused herein, “and/or” means that one, all, or any combination of itemsin a list separated by “and/or” are included in the list; for example“1, 2 and/or 3” is equivalent to “‘1’ or ‘2’ or ‘3’ or ‘1 and 2’ or ‘1and 3’ or ‘2 and 3’ or ‘1, 2 and 3’”.

Every formulation or combination of components described or exemplifiedcan be used to practice the invention, unless otherwise stated. Specificnames of materials are intended to be exemplary, as it is known that oneof ordinary skill in the art can name the same material differently. Oneof ordinary skill in the art will appreciate that methods, deviceelements, starting materials, and synthetic methods other than thosespecifically exemplified can be employed in the practice of theinvention without resort to undue experimentation. All art-knownfunctional equivalents, of any such methods, device elements, startingmaterials, and synthetic methods are intended to be included in thisinvention. Whenever a range is given in the specification, for example,a temperature range, a time range, or a composition range, allintermediate ranges and subranges, as well as all individual valuesincluded in the ranges given are intended to be included in thedisclosure.

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredient notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. Any recitation hereinof the term “comprising”, particularly in a description of components ofa composition or in a description of elements of a device, is understoodto encompass those compositions and methods consisting essentially ofand consisting of the recited components or elements. The inventionillustratively described herein suitably may be practiced in the absenceof any element or elements, limitation or limitations which is notspecifically disclosed herein.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this invention as defined by the appended claims.

We claim:
 1. A medical sensor comprising: a flexible or stretchable substrate; one or more flexible or stretchable light emitting diode (LED) arrays supported by said flexible or stretchable substrate, each flexible or stretchable LED array comprising one or more inorganic LEDs; one or more flexible or stretchable photodetector (PD) arrays supported by said flexible or stretchable substrate, each flexible or stretchable PD array comprising one or more inorganic semiconductor elements; an optical element in optical communication with the one or more LED arrays and/or the one or more PD arrays; one or more barrier layers partially encapsulating said one or more flexible or stretchable LED arrays, and said one or more flexible or stretchable PD arrays, wherein said barrier layer prevents fluid from said environment from contacting at least a portion of said inorganic LEDs of said one or more flexible or stretchable LED arrays and at least a portion of said inorganic semiconductor elements of said one or more flexible or stretchable PD arrays; wherein the one or more barrier layers comprise holes formed at selected regions of the one or more barrier layers, the selected regions corresponding to locations of at least some of the inorganic semiconductor elements; and a controller configured to measure blood oxygenation in tissue via electromagnetic radiation intensity information received from said one or more flexible or stretchable PD arrays.
 2. The medical sensor of claim 1, wherein said one or more flexible or stretchable LED arrays comprises one or more individually encapsulated LED array layers provided in a multilayer stacked geometry.
 3. The medical sensor of claim 1, wherein said one or more flexible or stretchable LED arrays comprises 2 to 1,000 individually encapsulated LED array layers provided in a multilayer laminated geometry.
 4. The medical sensor of claim 1, wherein said one or more flexible or stretchable PD arrays comprises one or more individually encapsulated PD array layers provided in a multilayer stacked geometry.
 5. The medical sensor of claim 1, wherein said one or more flexible or stretchable PD arrays comprises 2 to 1,000 individually encapsulated PD array layers provided in a multilayer laminated geometry.
 6. The medical sensor of claim 1, wherein said one or more flexible or stretchable LED arrays comprise a first array of LEDs that emit light of a first wavelength range and a second array of LEDs that emit light of a second wavelength range.
 7. The medical sensor of claim 6, wherein the LEDs of said first array are configured to emit red light and wherein the LEDs of said second array are configured to emit infrared light.
 8. The medical sensor of claim 6, wherein said first wavelength range includes light having a wavelength of 680 nm, and wherein said second wavelength range includes light having a wavelength of 940 nm.
 9. The medical sensor of claim 6, wherein the LEDs of said first array are laterally offset from the LEDs of said second array.
 10. The medical sensor of claim 1, wherein the controller is configured to operate said one or more LED arrays in short pulse mode.
 11. The medical sensor of claim 1, wherein the optical element comprises a coating, a reflector, a window, an optical filter, a collecting optic, a diffusing optic, a concentrating optic, or a combination thereof.
 12. The medical sensor of claim 1, wherein the optical element comprises a molded structure.
 13. The medical sensor of claim 1, wherein the optical element comprises a replica molded structure.
 14. The medical sensor of claim 1, wherein the optical element comprises a lithographically patterned structure.
 15. The medical sensor of claim 1, wherein the optical element comprises a structure patterned by nano-imprint lithography.
 16. The medical sensor of claim 1, wherein the optical element comprises a lens, a diffuser, a reflective coating, a reflective coating having a transparent section, a micro-structured grating, or a nanostructured grating.
 17. The medical sensor of claim 1, wherein the LED arrays comprise p-LEDs and wherein the PD arrays comprise ρ-IPDs.
 18. The medical sensor of claim 1, wherein the optical element comprises one or more plasmonic crystals.
 19. The medical sensor of claim 1, wherein the optical element comprises a plasmonic structure including a layer of Au sputter-deposited onto a thin polymer film.
 20. The medical sensor of claim 1, wherein the one or more barrier layers are mesh-structure barrier layers.
 21. The medical sensor of claim 1, wherein said barrier layer provides a net permeability with respect to transport of water in said biological environment to said flexible or stretchable device low enough to prevent an electrical short circuit in said flexible or stretchable electronic circuit or wherein said barrier layer provides a net leakage current from said flexible or stretchable electronic circuit to said tissue of 10 μA or less or 0.1 μA/cm2 or less.
 22. The medical sensor of claim 1, wherein said barrier layer is a moisture barrier which provides protection to components from water or other solvents.
 23. The medical sensor of claim 1, wherein said barrier layer comprises windows. 